ANDROID: rust_binder: reorganize process cleanup

This fixes some test failures in rustBinderTest caused by commit
f06dd0cd ("ANDROID: rust_binder: release threads before refs").
Honestly I'm not entirely sure why. Note that this reverses that commit,
and fixes the resulting logspam by instead moving cleanup of allocated
buffers to the end of process release.

Bug: 431914626
Change-Id: I1f7faa486f86cef7fbe37ad87b720573a5e05ee5
Signed-off-by: Alice Ryhl <aliceryhl@google.com>