Remove unused music commands that haven't been in LilyPond since 2.17.25

[ksnortum]

No description provided.

[fedelibre]

I guess that you took the list from this convert-ly rule.

I wonder if we should rather remove these lines instead of comment them.
@PeterBjuhr @jeanas what do you think?

[ksnortum]

I actually ran into two of them in the auto-complete function, then found the conversion rule as you said. I'm happy to remove the lines. I was just being "cowardly" in commenting them.

[fedelibre]

I think we should remove old syntax instead of commenting it. Please remove the lines.
You should also remove bracketCloseSymbol. Thanks

[fedelibre]

I think you have to git pull -r origin master in order to pass the CI checks.

[ksnortum]

Sorry for the commit history. git rebase still frightens me.

[fedelibre]

I've cleaned up the git history and pushed it to your branch. It is now ready to be merged.