addonsu: Fix installation on TWRP A/B

* These checks need to be added back otherwise it fails to
  extract files due to 'Too many symbolic links encountered' errors.
* Log:
Installing su addon...
Installing su addon...about to run program [/tmp/mount-system.sh] with 1 args
Extracted file "/system/xbin/su"
Extracted file "/system/addon.d/51-addonsu.sh"
failed to create dir for /system/etc/init/superuser.rc
script aborted: set_metadata: Error on lstat of "/system/etc/init/superuser.rc": Too many symbolic links encountered
set_metadata: Error on lstat of "/system/etc/init/superuser.rc": Too many symbolic links encounterederror: 25
cause: 111
Updater process ended with ERROR: 7

Change-Id: Ibf5082756063f7e703cbc47cf9642677983874ac
diff --git a/addonsu/updater-script-remove b/addonsu/updater-script-remove
index ba4fcaa..bd753a3 100644
--- a/addonsu/updater-script-remove
+++ b/addonsu/updater-script-remove
@@ -6,10 +6,17 @@
 set_metadata("/tmp/unmount-system.sh", "uid", 0, "gid", 0, "mode", 0755);
 run_program("/tmp/mount-system.sh") == 0 || abort("Could not mount /system");
 
-delete("/system/addon.d/51-addonsu.sh");
-delete("/system/bin/su");
-delete("/system/etc/init/superuser.rc");
-delete("/system/xbin/su");
+if getprop("ro.build.system_root_image") != "true" then
+  delete("/system/addon.d/51-addonsu.sh");
+  delete("/system/bin/su");
+  delete("/system/etc/init/superuser.rc");
+  delete("/system/xbin/su");
+else
+  delete("/system/system/addon.d/51-addonsu.sh");
+  delete("/system/system/bin/su");
+  delete("/system/system/etc/init/superuser.rc");
+  delete("/system/system/xbin/su");
+endif;
 
 run_program("/tmp/unmount-system.sh") == 0 || ui_print("Could not unmount /system");
 ui_print("Done");