Remove Nova Launcher as prebuilt

Signature issue removes the ability to update to current version(s). Default to only Launcher2
and allow user to decide to install third-party launcher (Apex, Nova, ADW, etc.)

Change-Id: I5f20d97be922b79701f2b288e57474e9cae4f79c
Signed-off-by: bmc08gt <bmc08gt.teamb00sted@gmail.com>

Conflicts:
	prebuilt/common/app/NovaLauncher.apk