Don't override the user's fonts

This patch is similar in spirit to rust-lang/blog.rust-lang.org#263 and
onur/docs.rs#240; it removes the specific font overrides in rustdoc.css
so that the browser will use the user's configured fonts. This reduces
the weight of all rustdoc pages (yay for mobile!) while also letting
users use whatever fonts they prefer.

The net result of the change is that the page will look less "uniform"
across different browsers, OSes, and devices, but the overall aesthetic
should be preserved. It also means that user preferences are respected,
and that legibility is improved for users with particular font needs, or
on platforms that sometimes gets confused about how to render fonts
nicely (ehrm, Linux).

Author: jonhoo

src/librustdoc/html/static/COPYRIGHT.txt

@@ -2,31 +2,6 @@ These documentation pages include resources by third parties. This copyright
 file applies only to those resources. The following third party resources are
 included, and carry their own copyright notices and license terms:
 
-* Fira Sans (FiraSans-Regular.woff, FiraSans-Medium.woff):
-
-    Copyright (c) 2014, Mozilla Foundation https://mozilla.org/
-    with Reserved Font Name Fira Sans.
-
-    Copyright (c) 2014, Telefonica S.A.
-
-    Licensed under the SIL Open Font License, Version 1.1.
-    See FiraSans-LICENSE.txt.
-
-* Heuristica (Heuristica-Italic.woff):
-
-    Copyright 1989, 1991 Adobe Systems Incorporated. All rights reserved.
-    Utopia is either a registered trademark or trademark of Adobe Systems
-    Incorporated in the United States and/or other countries. Used under
-    license.
-
-    Copyright 2006 Han The Thanh, Vntopia font family, http://vntex.sf.net
-
-    Copyright (c) 2008-2012, Andrey V. Panov (panov@canopus.iacp.dvo.ru),
-    with Reserved Font Name Heuristica.
-
-    Licensed under the SIL Open Font License, Version 1.1.
-    See Heuristica-LICENSE.txt.
-
 * rustdoc.css, main.js, and playpen.js:
 
     Copyright 2015 The Rust Developers.
@@ -38,22 +13,4 @@ included, and carry their own copyright notices and license terms:
     Copyright (c) Nicolas Gallagher and Jonathan Neal.
     Licensed under the MIT license (see LICENSE-MIT.txt).
 
-* Source Code Pro (SourceCodePro-Regular.woff, SourceCodePro-Semibold.woff):
-
-    Copyright 2010, 2012 Adobe Systems Incorporated (http://www.adobe.com/),
-    with Reserved Font Name 'Source'. All Rights Reserved. Source is a trademark
-    of Adobe Systems Incorporated in the United States and/or other countries.
-
-    Licensed under the SIL Open Font License, Version 1.1.
-    See SourceCodePro-LICENSE.txt.
-
-* Source Serif Pro (SourceSerifPro-Regular.woff, SourceSerifPro-Bold.woff):
-
-    Copyright 2014 Adobe Systems Incorporated (http://www.adobe.com/), with
-    Reserved Font Name 'Source'. All Rights Reserved. Source is a trademark of
-    Adobe Systems Incorporated in the United States and/or other countries.
-
-    Licensed under the SIL Open Font License, Version 1.1.
-    See SourceSerifPro-LICENSE.txt.
-
 This copyright file is intended to be distributed with rustdoc output.

src/librustdoc/html/static/FiraSans-Medium.woff

@@ -10,57 +10,6 @@
  * except according to those terms.
  */
 
-/* See FiraSans-LICENSE.txt for the Fira Sans license. */
-@font-face {
-	font-family: 'Fira Sans';
-	font-style: normal;
-	font-weight: 400;
-	src: local('Fira Sans'), url("FiraSans-Regular.woff") format('woff');
-}
-@font-face {
-	font-family: 'Fira Sans';
-	font-style: normal;
-	font-weight: 500;
-	src: local('Fira Sans Medium'), url("FiraSans-Medium.woff") format('woff');
-}
-
-/* See SourceSerifPro-LICENSE.txt for the Source Serif Pro license and
- * Heuristica-LICENSE.txt for the Heuristica license. */
-@font-face {
-	font-family: 'Source Serif Pro';
-	font-style: normal;
-	font-weight: 400;
-	src: local('Source Serif Pro'), url("SourceSerifPro-Regular.woff") format('woff');
-}
-@font-face {
-	font-family: 'Source Serif Pro';
-	font-style: italic;
-	font-weight: 400;
-	src: url("Heuristica-Italic.woff") format('woff');
-}
-@font-face {
-	font-family: 'Source Serif Pro';
-	font-style: normal;
-	font-weight: 700;
-	src: local('Source Serif Pro Bold'), url("SourceSerifPro-Bold.woff") format('woff');
-}
-
-/* See SourceCodePro-LICENSE.txt for the Source Code Pro license. */
-@font-face {
-	font-family: 'Source Code Pro';
-	font-style: normal;
-	font-weight: 400;
-	/* Avoid using locally installed font because bad versions are in circulation:
-	 * see https://github.com/rust-lang/rust/issues/24355 */
-	src: url("SourceCodePro-Regular.woff") format('woff');
-}
-@font-face {
-	font-family: 'Source Code Pro';
-	font-style: normal;
-	font-weight: 600;
-	src: url("SourceCodePro-Semibold.woff") format('woff');
-}
-
 * {
   -webkit-box-sizing: border-box;
 	 -moz-box-sizing: border-box;
@@ -70,7 +19,7 @@
 /* General structure and fonts */
 
 body {
-	font: 16px/1.4 "Source Serif Pro", Georgia, Times, "Times New Roman", serif;
+	font-size: 1em;
 	margin: 0;
 	position: relative;
 	padding: 10px 15px 20px 15px;
@@ -115,7 +64,7 @@ h3.impl, h3.method, h3.type {
 h1, h2, h3, h4,
 .sidebar, a.source, .search-input, .content table :not(code)>a,
 .collapse-toggle, div.item-list .out-of-band {
-	font-family: "Fira Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;
+	font-family: sans-serif;
 }
 
 ol, ul {
@@ -134,7 +83,7 @@ summary {
 }
 
 code, pre {
-	font-family: "Source Code Pro", Menlo, Monaco, Consolas, "DejaVu Sans Mono", Inconsolata, monospace;
+	font-family: monospace;
 	white-space: pre-wrap;
 }
 .docblock code, .docblock-short code {
@@ -395,7 +344,7 @@ h4 > code, h3 > code, .invisible > code {
 }
 #main > .since {
 	top: inherit;
-	font-family: "Fira Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;
+	font-family: sans-serif;
 }
 
 .content table:not(.table-display) {
@@ -1272,7 +1221,7 @@ h3.important {
 kbd {
 	display: inline-block;
 	padding: 3px 5px;
-	font: 15px "SFMono-Regular", Consolas, "Liberation Mono", Menlo, Courier, monospace;
+	font: 0.9rem monospace;
 	line-height: 10px;
 	vertical-align: middle;
 	border: solid 1px;