Issue 5917: ly:performance-headers and \midi { after-writing } (issue 567450043 by nine.fierce.ballads@gmail.com)

[lemzwerg--- via Discussions on LilyPond development]

LGTM


https://codereview.appspot.com/567450043/diff/555680043/lily/performance-scheme.cc
File lily/performance-scheme.cc (left):

https://codereview.appspot.com/567450043/diff/555680043/lily/performance-scheme.cc#oldcode31
lily/performance-scheme.cc:31: LY_DEFINE (ly_performance_set_header_x,
"ly:performance-set-header!",
Will this removal need a `convert-ly` warning?

https://codereview.appspot.com/567450043/