Change `buck clean` so that it does not delete files that IntelliJ is interested in.

Summary:
We do not want `buck clean` to delete files that IntelliJ indexes by default
because empirically, `buck clean` currently throws IntelliJ into a tizzy.

Test Plan:
Ran `buck clean`.
Verify that buck-out/bin and buck-out/gen were deleted
and that buck-out/annotation and buck-out/android still exist.