[REVIEW-3-6] fix for fdo#54074, fdo#53364 and maybe for fdo#49520, don't delete broadcasters in formula cells twice

[Markus Mohrhard]

Hey,

[1] fixes a serious bug in calc that happens in a formula cell with a
broadcaster that has listeners is deleted. The problem is that the
Broadcaster is deleted twice. Once as part of the ScFormulaCell and
once as part of the ScNoteCell that is used as replacement for the
ScFormulaCell.

We need to release the broadcaster from ScFormulaCell because the
ScNoteCell is taking over control and is only there to keep track of
the Broadcaster.

Regards,
Markus

[1] http://cgit.freedesktop.org/libreoffice/core/commit/?id=7a8040665f40fbcb4fa58c036aa066f061abd9ba