we need the SdrPage for deleting the notes, fdo#86166

The SdrPage that contains the shapes for the note captions is deleted
before the notes. Prevent that case by deleting the notes before
deleting the SdrPage.

Change-Id: I13727cea7df0b033fb386a6a8e20dcadec743335
Reviewed-on: https://gerrit.libreoffice.org/13362
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>