[TASK] Remove dead code in VidiDbBackend

In the first round, code was taken
from Typo3DbBackend with minimum
adjustments for Vidi. However, some part
are not used at all such as update, add, ...
Those parts can be safely removed.

Change-Id: Ic7bd2f5a3c1cd736ac01db920854e8bc6cf041f5
Releases: 0.4.0
Resolves: #59079