Fix output switcher will show 2 media session in some use cases

Before this CL, we didn't check whether the remote session existed
in the list before. If priority of remote session is higher than
local session, it causes us to return the local session even if
the list has a remote session.

This CL uses a list to cache package names of remote sessions.
If the local session has the same package name of the remote session
then don't return the local session.

Bug: 169052790
Test: make -j42 RunSettingsRoboTests
Change-Id: I2726a3deb397f646e4c74a8c445dde6fafb694a8