Refactor ServiceWatcher

1) Take advantage of new binder callback APIs to simplify ServiceWatcher
internally
2) Move resources into subclasses instead of LMS
3) Rename some public APIs of ServiceWatcher
4) Completely remove the signature checking done within ServiceWatcher
and LMS. It doesn't appear to serve any useful purpose anymore, and it's
debatable if it ever did anything useful. Rather than restricting bound
services to a set of packages + packages that share a signature with
those packages at boot, restrict to system packages only.
5) Remove unused config values

Test: presubmits
Change-Id: I870043539d0f96fe443a1da238d109c3fa1930c9