remove SvRefBase::QueryDelete

Move it's functionality into the only place that needs it, in the dbase
driver.
Removes an extra virtual call from a widely used class.
The dbase driver seems to be using to perform some kind of whacky object
recycling, so it's not like we want this functionality to be used
somewhere else.

Change-Id: I41018f71e0b0a79fdd3d527536f0ac95c788e614
Reviewed-on: https://gerrit.libreoffice.org/11786
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>