Avoid creating two <title>s

[Kestrer]

docs.rs creates two titles for most pages, the Rustdoc title and docs.rs title:

This is invalid HTML and causes my browser to sometimes just display the URL on the titlebar, since it doesn't know which title to use.

I would actually prefer to use just the Rustdoc title because it provides more information about the site.

[jyn514]

This is fallout from #930. If we're just using the rustdoc title this should be pretty easy, just remove this line:

docs.rs/templates/rustdoc/head.html

Line 11 in 1107e9b

<title>{{ macros::doc_title(name=krate.name, version=krate.version) }}</title>