vendor/lineage: Drop obsolete TW_EXCLUDE_SUPERSU flag

* Reference commits:
* https://gerrit.omnirom.org/#/c/android_bootable_recovery/+/31609/
* https://gerrit.omnirom.org/#/c/android_bootable_recovery/+/31745/

Change-Id: I7efbdc3ebee29095b36612660e065b6d7c603a93
diff --git a/config/twrp.mk b/config/twrp.mk
index 845e2e2..6f75540 100644
--- a/config/twrp.mk
+++ b/config/twrp.mk
@@ -1,2 +1 @@
 RECOVERY_VARIANT := twrp
-TW_EXCLUDE_SUPERSU := true