This fixes OSX "make debugrun" by dropping VCL_HIDE_WINDOWS
handling and removing the internal GetPseudoHeadless() API.

While at it moves the DialogCancelMode enum out of Application.

Change-Id: I4876e752ddbfc39dd44faa673fb0e97810089a75
Reviewed-on: https://gerrit.libreoffice.org/61598
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>