Remove superfluous AnimationController::suspend/resumeAnimations()

These methods were added to provide the embedder (of WebKit) with control over
animations. However, this functionality is not used by Chromium.

The only users of these methods are the corresponding methods on the Internals
testing object, but these exist simply to allow this functionality to be
exercised in tests (https://bugs.webkit.org/show_bug.cgi?id=43733).

Note GraphicsLayer::suspendAnimations() is used by Internals::pauseAnimations(),
so is still required.

This change also removes all of the tests of this functionality, most of which
are either broken or flaky anyway.

A later change to Chromium will remove the implementation of
WebLayer::resumeAnimations(), which is no longer required.

BUG=248938,243353,62138,61739
R=dstockwell@chromium.org, tkent@chromium.org, dstockwell

Review URL: https://codereview.chromium.org/27589003

git-svn-id: svn://svn.chromium.org/blink/trunk@160040 bbb929c8-8fbe-4397-9dbb-9b2b20218538