git cl: no longer support --rietveld flag when forcing codereview.

R=ehmaldonado

Bug: 770408
Change-Id: I980487aacd115535d0ca855cd1edfcfc18fc5cbe
Reviewed-on: https://chromium-review.googlesource.com/c/1279138
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
diff --git a/git_cl.py b/git_cl.py
index 9aa1b77..e8c910a 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -3288,13 +3288,11 @@
 
 
 def _process_codereview_select_options(parser, options):
-  if options.gerrit and options.rietveld:
-    parser.error('Options --gerrit and --rietveld are mutually exclusive')
+  if options.rietveld:
+    parser.error('--rietveld is no longer supported')
   options.forced_codereview = None
   if options.gerrit:
     options.forced_codereview = 'gerrit'
-  elif options.rietveld:
-    options.forced_codereview = 'rietveld'
 
 
 def _get_bug_line_values(default_project, bugs):