Simplifying logic for managed for icon addition

> Checking for duplicate icons before adding new icons

For O and above, icon addition is controlled using
SessionCommitReceiver.
As long as the Launcher is the default app, it will keep adding
icons on the homescreen. Apps installed while launcher was
not the default homescreen, no icons will be added.

For below O, icons are added based on package event. As long as
the Launcher process is running, it will keep adding icons on the
homescreen. Apps installed while the launcher app was dead, no
icons will be added.

Bug: 37528649
Bug: 37082950
Bug: 34112546
Change-Id: Ic99501fa476c00474a479f2a36c24614bfa3f4bf