[TASK] Remove db setup from .travis.yml

With proper mocking in place we no longer need an
initialized database to run unit tests.

Change-Id: I3913186540bbd1b1419c37132cddaaa34ea9ca34
Related: #51436
Releases: 6.2
Reviewed-on: https://review.typo3.org/28645
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn