Fix update_prebuilts.py

Remove reference to args.stx left by If2d2369387e57c1e35d35b5982475d5970169980.

Test: ./update-prebuilts.py -p 6500461
Change-Id: Ifb37cc24fa0535c3918cc66ba4a1df39147063a8
Merged-In: I7c2e9b09ab0de36e352db16186288b0c4908f7b4
diff --git a/update_prebuilts/update_prebuilts.py b/update_prebuilts/update_prebuilts.py
index 953fe2d..4e17773 100755
--- a/update_prebuilts/update_prebuilts.py
+++ b/update_prebuilts/update_prebuilts.py
@@ -692,10 +692,6 @@
     '--commit-first', action="store_true",
     help='If specified, then if uncommited changes exist, commit before continuing')
 args = parser.parse_args()
-if args.stx:
-    args.androidx = True
-else:
-    args.androidx = False
 args.support = False
 args.file = True
 if not args.source: