tree-wide: drop copyright headers from frequent contributors

Fixes #9320.

for p in Shapovalov Chevalier Rozhkov Sievers Mack Herrmann Schmidt Rudenberg Sahani Landden Andersen Watanabe; do
  git grep -e 'Copyright.*'$p -l|xargs perl -i -0pe 's|/([*][*])?[*]\s+([*#]\s+)?Copyright[^\n]*'$p'[^\n]*\s*[*]([*][*])?/\n*|\n|gms; s|\s+([*#]\s+)?Copyright[^\n]*'$p'[^\n]*\n*|\n|gms'
done

shell-completion/bash/bootctl

@@ -3,7 +3,6 @@
 #
 # This file is part of systemd.
 #
-# Copyright 2014 Thomas H.P. Andersen
 #
 # systemd is free software; you can redistribute it and/or modify it
 # under the terms of the GNU Lesser General Public License as published by