scripts: cros_gdb: mark --remote_pid deprecated properly

We deprecated this option by changing the help text, but didn't use
any other communication strategy for users to realize they shouldn't
use it.  Use the new deprecated= argument instead.

BUG=None
TEST=CQ passes

Change-Id: I0721b331e5862044f4acc59cbe3375e74713fa34
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4436750
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_gdb.py b/scripts/cros_gdb.py
index d33280c..ccfca99 100644
--- a/scripts/cros_gdb.py
+++ b/scripts/cros_gdb.py
@@ -670,11 +670,12 @@
         help="Process ID of the (already) running process on the"
         " remote device to which to attach.",
     )
+    # TODO(build): Delete in Jan 2024.
     parser.add_argument(
         "--remote_pid",
         dest="pid",
-        default="",
-        help="Deprecated alias for --pid.",
+        help=argparse.SUPPRESS,
+        deprecated="Use --pid instead.",
     )
     parser.add_argument(
         "--no-ping",