Revert^2 "libbinder: introduce guards for getCalling*"

df2e017a

Rein in the context! These "global" functions make sense sometimes, and
sometimes they make NO sense. Specifically, if you're going to make a
binder RPC call, you shouldn't be relying on getCalling* (silly!).

This is added as a generic mechanism in order that it might see more
use.

Bug: 186647790
Test: binderLibTest

Change-Id: Ic64bde4e8e0d6b203f58eef1ba09f2229ad2008b