Undeprecate animation background color

Now that we support showing a background color behind animations again
to makes sense to undeprecate the background color animation API so the
background color can be set during in the animation's definition.

Test: atest CtsWindowManagerDeviceTestCases:ActivityTransitionTests
Change-Id: I1bd1468f7ae4ee41f5d2d25947852c78b93bc6ee