Fixing "id.ly" regtest file

[Paul]

Hi all,

I pushed my commits for issue 4974 to staging, and all went well, but 
then I noticed that the regtest "id.ly" was incorrect.  The diff for it has:

-{ \override NoteHead.id = #"foo" c }
+{ \override NoteHead.output-attributes.id = #"foo" c }

when this shouldn't have been changed.  (Running the 
scripts/auxiliar/...  convert-ly script made this change but I 
overlooked it because the header text in that file was also changed 
manually.  So I didn't manually correct it.)

To fix this, I'd propose reverting the last commit on master:
http://git.savannah.gnu.org/cgit/lilypond.git/commit/?id=03d47798d39bd9ce2a87376ea1585f1f31c1b81b

and then I can re-upload an amended version of that commit that fixes 
the "id.ly" file.  Please let me know how best to proceed.

Sorry for not catching this before,
-Paul