common-mk: Remove the arc variable

This is the cleanup step for
https://chromium-review.googlesource.com/#/c/372921/ .

CQ-DEPEND=CL:365122,CL:376921
BUG=b:30230518
TEST=emerge chromeos-base/chromeos-login

Change-Id: Ic25ec5a378d2c18cc2b42de86b2d8868d25da185
Reviewed-on: https://chromium-review.googlesource.com/376845
Commit-Ready: Luis Hector Chavez <lhchavez@google.com>
Tested-by: Luis Hector Chavez <lhchavez@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/common-mk/common.gypi b/common-mk/common.gypi
index e79187c..ba7dfb9 100644
--- a/common-mk/common.gypi
+++ b/common-mk/common.gypi
@@ -21,7 +21,6 @@
     # DON'T EDIT BELOW THIS LINE.
     # You can declare new variables, but you shouldn't be changing their
     # default settings.  The platform python build helpers set them up.
-    'USE_arc%': 0,
     'USE_cheets%': 0,
     'USE_attestation%': 0,
     'USE_binder%': 0,