Only filter when remote session has associated notification

Bug: 167706409
Test: manual - Cast from Google Play Books and check that media controls
are available in QS.

Change-Id: Ifc404be2de6f5f87a1d43e3b51d3ca00c73c6e06
(cherry picked from commit 8cc72bdf)
Merged-In: Ifc404be2de6f5f87a1d43e3b51d3ca00c73c6e06