FORMS : Remove usage of DBG_CTOR and DBG_DTOR.

Valgrind is capable of detecting such bugs. No need for extra macros.

Change-Id: Ida618d6ac383c65f1c09212a7b6aa5ee228677db
Reviewed-on: https://gerrit.libreoffice.org/7534
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>