[TASK] Typo3DbBackend, getRowsFromResult(): Drop source-argument

Only an internal function and $source is not used.

Resolves: #47187
Releases: 6.1
Change-Id: I8c3672d3dafc033a0b3a3c9292845c4e92dc4946
Reviewed-on: https://review.typo3.org/19917
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer