WindowInsetsAnimationTests: Remove @FlakyTest after test was fixed

After I966c35fdcdf29670a68d4e11e613bc7f811a40e8, this test should
be reliable and can be re-enabled.

Change-Id: I649e651c3f6f9af478ac0e97ce8e8671c6d9539a
Fixes: 159038873
Test: atest WindowInsetsAnimationTests
1 file changed