Lose pointless per-db and per-dbi errfile and errcall pointers

Lose pointless per-db and per-dbi errfile and errcall pointers
- BDB uses stderr for errfile when not set, which is what we set it
  to through various hoops. Just leave it alone.
- db_errcall has always been (intentionally) NULL to disable that output,
  the errors get logged though cvtdberr() with slight filtering