Revert "[LCP] Add animated image support"

This reverts commit b7d510c06e0436cfb4bd7260175cd460b949225c.

Reason for revert: speculative revert for new flakiness in
PageLoadMetricsBrowserTestWithAnimatedLCPFlag, see first failing
build
https://ci.chromium.org/p/chromium/builders/ci/Linux%20Tests%20%28dbg%29%281%29/99853

Original change's description:
> [LCP] Add animated image support
>
> This CL adds support for better handling of animated images in LCP:
> * A new attribute is exposing the first animated frame's paint time
> (behind a flag).
> * `startTime` is not changed.
> * The PageLoadMetrics reported for LCP are set to that first frame paint
> time for animated images (behind another flag).
> * Entries are not emitted until the image is loaded.
>
> Relevant spec issue:
> w3c/largest-contentful-paint#83
>
> Change-Id: I6bb01eacb4f200f9c032ffcfcd9a1a41126a7773
> Bug: 1260953
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3226157
> Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
> Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#935133}

Bug: 1260953
Change-Id: I00878689de95de38645195da81c6baf577d868a6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3247071
Auto-Submit: Mikel Astiz <mastiz@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Owners-Override: Mikel Astiz <mastiz@google.com>
Cr-Commit-Position: refs/heads/main@{#935350}

largest-contentful-paint/resources/largest-contentful-paint-helpers.js

@@ -1,6 +1,3 @@
-const image_delay = 1000;
-const delay_pipe_value = image_delay / 1000;
-
 // Receives an image LargestContentfulPaint |entry| and checks |entry|'s attribute values.
 // The |timeLowerBound| parameter is a lower bound on the loadTime value of the entry.
 // The |options| parameter may contain some string values specifying the following:
@@ -36,33 +33,4 @@ function checkImage(entry, expectedUrl, expectedID, expectedSize, timeLowerBound
   } else {
     assert_equals(entry.size, expectedSize);
   }
-  if (options.includes('animated')) {
-    assert_greater_than(entry.loadTime, entry.firstAnimatedFrameTime,
-      'firstAnimatedFrameTime should be smaller than loadTime');
-    assert_greater_than(entry.renderTime, entry.firstAnimatedFrameTime,
-      'firstAnimatedFrameTime should be smaller than renderTime');
-    assert_less_than(entry.firstAnimatedFrameTime, image_delay,
-      'firstAnimatedFrameTime should be smaller than the delay applied to the second frame');
-    assert_greater_than(entry.firstAnimatedFrameTime, 0,
-      'firstAnimatedFrameTime should be larger than 0');
-  }
-  if (options.includes('animated-zero')) {
-    assert_equals(entry.firstAnimatedFrameTime, 0, 'firstAnimatedFrameTime should be 0');
-  }
 }
-
-const load_and_observe = url => {
-  return new Promise(resolve => {
-    (new PerformanceObserver(entryList => {
-      for (let entry of entryList.getEntries()) {
-        if (entry.url == url) {
-          resolve(entryList.getEntries()[0]);
-        }
-      }
-    })).observe({type: 'largest-contentful-paint', buffered: true});
-    const img = new Image();
-    img.id = 'image_id';
-    img.src = url;
-    document.body.appendChild(img);
-  });
-};