libbinder_ndk: don't preserve positive statuses

This was a bug introduced during the development of this code when
positive errors were considered service specific errors. This isn't
actually how the API works, but when later patchsets were added, the
code being removed here wasn't removed.

Bug: 111445392
Test: atest android.binder.cts
Change-Id: I83e06fa8f0d76dfba35f9b2d971e5491c103ee70