Add ROM version tag to build property and delete ro.pa

Adding the version tag to the build.prop property will display it in Settings ->
About -> PA Version

Remove ro.pa property because it is no longer used by OTA.

Change-Id: I6636ae500eef236d018a5c4b13e7081dae4518c6
Signed-off-by: Evan Anderson <evan1124@gmail.com>