Fix skip epoll flag behavior

Address a bug where we previously mistakenly made the flag a no-op.
Remove the holdback flag, because it's no longer necessary (we're going to rollback the primary flag).

Bug: 458115020
Flag: android.os.native_looper_skip_epoll_wait_for_zero_timeout
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:0b4c21a58bdf15d8ff1022e13998450668c43c5f
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:1094b69d470f29d25dbb9b7a2f9f4974b63ba0f9
Merged-In: I9bf21bfef8ac2bf18df164901d92935297e84036
Change-Id: I9bf21bfef8ac2bf18df164901d92935297e84036