Remove __linux__ ifdefs where not needed

The downstream branches now know about Parcel and binder, so in some
places, these #ifdef statements are not needed.

This CL should help reduce the divergence with downstream efforts. See
the merge conflict resolution CL as an example:
https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/native/+/27201796/-2..3

Bug: 309829647
Test: presubmit
Change-Id: Iec17cface5069ca79a565c205546db8ada8a07ee