We don't usually mass-remove trailing whitespace from the actual source
code because it would complicate cherry-picking bug fixes to older
branches, but that reasoning doesn't really apply to the comments
containing copyright and licensing notices.

Removing trailing whitespace makes it much easier to move code around:
we have a commit hook that rejects commits containing trailing
whitespace, but that commit hook counts moving a file as a delete + add
pair, so it objects to moving code that contains trailing whitespace.

Signed-off-by: Simon McVittie <smcv@collabora.com>