Serial: Remove global ReportBadMessage(), GetMessageCallback()

This patch migrates the global ReportBadMessage(), GetMessageCallback()
to their respective equivalent on mojo::Receiver.

Bug: 1213505
Change-Id: I3e5a180dcab86526385fb99c4e8d3a057cfd9018
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3114546


Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#918730}