[pmd][gc] Always retain the system package FAR

During an OTA the current system package meta FAR reference from
the static index could be overwritten and a subsequent GC would
remove the file. Now GC always excludes the system package meta
FAR from collection directly.

TEST=modify updater to abort early, verify system meta FAR is
collected. Apply this change, verify system meta FAR is retained

PKG-413 #done

Change-Id: I299729077d761bf09611aa21ce44f0db80909b11
1 file changed