Revert "Correct nullability and final constraints on new APIs."

This reverts commit b6940c3e.

Reason for revert: There appears to be a downstream issue with how the test API definitions are created; until I can figure out how to account for this I'll revert in AOSP (this is in internal master and its fine there).

Change-Id: I840c3ed82afa18323408e161913a84858f7a1539