gapps: Add AndroidMigratePrebuilt

* On Custom ROM's on Pixels, the downloading of
  this app by SetupWizard often hangs up,
  and needs to be restarted. Ship this to avoid
  that.

* Added to LOWMEM checkas it isn't necessary.

build/meta/com/google/android/update-binary

@@ -85,6 +85,7 @@ cd system
 
 if [ "$MEM" -lt "$LOWMEM" ]; then
   ui_print "Low RAM device detected, removing large extras"
+  exec_util "rm -rf priv-app/AndroidMigratePrebuilt"
   exec_util "rm -rf priv-app/SetupWizard"
   exec_util "rm -rf priv-app/Velvet"
 fi