MediaRouter2: Unify terms (select, add, group) to 'select'

This CL unifies the different terms ([select, add, group] route)
which actually have the same meaning - into 'select'.

Same applies for ([deselect, remove]) -> deselect.

Bug: 146400872
Test: atest mediaroutertest
Change-Id: Ic985359dd53f8b30bba654e6a451fcdf3be6cf24