Inline shouldDisableMediaOutput into Settings app

This allows the removal of a MediaRouter2Manager reference in
SettingsLib. Eventually, the inlined methods should be replaced with an
appropriate long-term alternative through SettingsLib.

This is a non-functional change.

Bug: 192657812
Test: Presubmit
Change-Id: I9f5dd6720fd95389335fec9e0689a40d88d30d46