[BUGFIX] ext:dbal Usage of dropped constant TYPO3_db

Usage of TYPO3_db constant prevents successful connection,
use database name directly instead.

Change-Id: I9017db927a8c58b5573964ad61ecce5c264abb34
Resolves: #77613
Releases: master
Reviewed-on: https://review.typo3.org/49567


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>