trivial: Remove trailing whitespace from copyright notices
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.
@rhabacker objected to commits in !1 (merged) removing this trailing whitespace when they moved modules around, so I'm mass-removing it from the copyright headers instead. We'll still need to remove trailing whitespace from the actual code on a case-by-case basis to avoid breaking