Clean up hasSystemFeature binder cache

Bug: 140788621

This is a non-functional clean-up.
1. Rename the classes and methods used by the binder cache so that
   everything public is based off of the binder name "hasSystemFeature".
2. Modified the hashCode() method to conform to the comments in cl/9965760

Test: Built a debug image and ran one iteration of MPTS.  Verified that no
errors were seen.

Change-Id: I3ffdda43a7dbe30a12449ff346e1e22b379ee308