edify: fix the RunBackup function

Remove 'self.UnpackPackageDir(system/addon.d, /system/addon.d)'
since this would overwrite any existing backup script e.g. gapps

Extract functions file to /tmp to not break existing
backup script files that rely on that file beeing in /tmp

Change-Id: I16741c17f30c28f5d537c693eaf43879d08f7ac1