Disable uninstall/disable for system apps

Disable the "remove" button for unused apps if the app is a system app.

This also disables the button on Auto. On TV, there was no functionality
to remove from the Unused Apps page to begin with.

Bug: 224018624
Test: atest AppHibernationIntegrationTest
Change-Id: I66ef2bf995d1eecf36eb43e52bac374b933cd96b