fix #292851: Note still played after having been deleted.

[mattmcclinch]

Resolves: https://musescore.org/en/node/292851.

This fixes the problem by adding a call to Score::setPlaylistDirty() when a note is removed from its chord, and when a chord is removed from its segment.

[dmitrio95]

This fix leaves a similar issue on undoing the note removal operation. That is, the following works incorrectly:

1. Remove a note from a chord
2. Click on some note before that chord, start/stop playback
3. Click on some note before that chord again
4. Undo
5. Play

Maybe similar setPlaylistDirty calls are also needed on adding notes and chords to a score.

[mattmcclinch]

Good point. Somehow I had missed that scenario during testing. I just pushed a change that does what you suggest.