Don't remove preferred activities when in power off alarm mode

When in power off alarm mode, only power off alarm apps are installed.
So some applications with preferred activity may not be installed. Don't
remove preferred activities when in power off alarm mode to avoid choosing
preferred activities again during next boot-up.

CRs-Fixed: 1063320
Change-Id: Ia383ce3ecc7fb5051c00211b007acd7123124a4c