Remove Create() that return an instance through MakeGarbageCollected in renderer/core/animation

As advised in [1], this CL removes unnecessary Foo::Create() factory functions
which return an instance using MakeGarbageCollected<Foo> in
//third_party/blink/renderer/core/animation, then this CL makes the callers
use MakeGarbageCollected<Foo> instead of Foo::Create() factory functions.

[1] https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/iJ1bawbxbWs/vEdfT5QtBgAJ

Bug: 939691
Change-Id: Ib1f8ce69ecc85f74a6f534d2c97b5d11b8fba7c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535469
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoung@igalia.com>
Cr-Commit-Position: refs/heads/master@{#643773}
4 files changed