scripts: cros_merge_to_branch: convert to common --dry-run options

BUG=None
TEST=CQ passes

Change-Id: Ia3914be32480a8f24c4de3980aad229ea6eca35d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4219580
Reviewed-by: Gilberto Contreras <gcontreras@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_merge_to_branch.py b/scripts/cros_merge_to_branch.py
index 1502241..deb2112 100644
--- a/scripts/cros_merge_to_branch.py
+++ b/scripts/cros_merge_to_branch.py
@@ -52,7 +52,7 @@
 
 def _GetParser():
     """Returns the parser to use for this module."""
-    parser = commandline.ArgumentParser(description=__doc__)
+    parser = commandline.ArgumentParser(description=__doc__, dryrun=True)
     parser.add_argument(
         "-d",
         "--draft",
@@ -61,14 +61,6 @@
         help="upload a draft to Gerrit rather than a change",
     )
     parser.add_argument(
-        "-n",
-        "--dry-run",
-        default=False,
-        action="store_true",
-        dest="dryrun",
-        help="apply changes locally but do not upload them",
-    )
-    parser.add_argument(
         "-e",
         "--email",
         help="use this email instead of the email you would "