Re-throw unexpected RemoteExceptions in MediaRouter

This change re-throws exceptions that can only be caused by a dead
system server. We avoid spamming the logs by just re-throwing.
This makes it more clear that the MediaRouter instance does not
end the method execution in a consistent state.

Bug: b/259025372
Test: atest MediaRouterTest
Change-Id: I28dbe7936e199e322dc634a8bcc2206afbc0eaf7