[CLEANUP] #4019 Drop lib/tx_realty_constants.php

Change-Id: If9a24296139e4b441a8a33d8d808875dfc09653c
Reviewed-on: http://review.typo3.org/34896
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>