This keyword is not expanded by Git which means it's not replaced with the
correct revision value in the releases made using git-based scripts and it's
confusing to have lines with unexpanded "$Id$" in the released files. As
expanding them with Git is not that simple (it could be done with git archive
and export-subst attribute) and there are not many benefits in having them in
the first place, just remove all these lines.

If nothing else, this will make an eventual transition to Git simpler.

Closes #14487.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74602 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775