Don't sign cLock with the platform certificate.

There is no need for it, and doing it prevents cLock from being
disableable, which some people might want to do.

Change-Id: I1ec8bab477754da26bbd64b2fbb283cf3fa912a5
JIRA:CYAN-1394
Merge branch 'cm-10.1' of github.com:CyanogenMod/android_packages_apps_LockClock into cm-10.1