Remove AnimationEdgeExtensionTests and AnimationBackgroundTests

We now have tests in ActivityTransitionTests which run exactly these
tests but are more polished and stable. The same change was first
applied in tm-qpr-dev and has been merged to the aosp master.

Test: ActivityTransitionTests

Bug: 233374447
Bug: 258990770
Change-Id: I27574365cd3564606cd0e95483d20318cd44ff59
Merged-In: I95f8233e889c56bb3fde0e0fc17099013ef28ce5