Stubs: Disable Errorprone warnings

The stubs are auto-generated and lack lots of annotations. Furthermore,
the originating code will already lead to warnings. So suppress all
Errorprone warnings for stub code.

Test: m
Test: m javac-check RUN_ERROR_PRONE=true
Change-Id: I214f348e2ecef5d640fa488f3d4cf9a18b942430