Remove pixel diff thresholds on NTP tests

Now that render tests are disabled on Android CFI bot
(crrev.com/c/2154730), remove pixel diff thresholds that were added to
address those failures.

Bug: 1068294
Change-Id: I3ef98cfec4e183c54bf3c754089a2463282e634c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2155011Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760223}

chrome/android/feed/core/javatests/src/org/chromium/chrome/browser/feed/FeedNewTabPageCardRenderTest.java

@@ -96,9 +96,6 @@ import java.util.List;
         mNtp = (FeedNewTabPage) mTab.getNativePage();
         mTileGridLayout = mNtp.getView().findViewById(R.id.tile_grid_layout);
         Assert.assertEquals(mSiteSuggestions.size(), mTileGridLayout.getChildCount());
-
-        // Set 10 diff threshold. It is a value in RGBA channel, not pixel count.
-        mRenderTestRule.setPixelDiffThreshold(10);
     }
 
     @Test

chrome/android/javatests/src/org/chromium/chrome/browser/ntp/NewTabPageTest.java

@@ -185,9 +185,6 @@ public class NewTabPageTest {
         mFakebox = mNtp.getView().findViewById(R.id.search_box);
         mTileGridLayout = mNtp.getView().findViewById(R.id.tile_grid_layout);
         Assert.assertEquals(mSiteSuggestions.size(), mTileGridLayout.getChildCount());
-
-        // TODO(crbug.com/1068294): Remove the following line if this general issue is fixed.
-        mRenderTestRule.setPixelDiffThreshold(10);
     }
 
     @After