cleanup of the use of rowcount

The way we handled rowcount for the results of a query was somewhat hacky and didn't work with
newer versions of SqlAlchemy and Oracle. As rowcount was only used in one place in the code and
it wasn't even needed there, I completely removed the rowcount field and the hacky code.
Merge pull request #5286 from hufnagel/rowcount-cleanup

cleanup of the use of rowcount