Fix #12116 update accidentals of tied back note when tie is deleted

Added call to updateAccidentals() in Chord::remove(Element*) and Note::remove(Element*) to make sure, notes which are no longer tied back get needed accidentals.

About undo.cpp:
Also added this call to RemoveElement::undo()

Let RemoveElement::undo() reset the tieBack property of the tie's endNote when restoring a removed tie.

Moved section to setTieBack(0) for endNotes of removed ties from RemoveElement::RemoveElement(Element*) to RemoveElement::redo(): This makes sure redo will bring the score back to the same state as the original delete command.

Remark: I'm not sure if the section after
// remove any slurs pointing to this chor/rest
should stay in RemoveElement::RemoveElement(Element*) for the same reason.