Clean generated source dir if .proto/.rs is gonee.

Similar to how we clean the generated source dir if .aidl becomes
obsolete.

Bug: 26688474
Change-Id: I66c5b6d6513259b5f4f4bac84f384f4bf953d82a
(cherry-pick from commit d5ffec938344defd437d8e315d6a3376b1100a5a)
2 files changed