Use sql-mode's font-lock for checking

Note that this requires a sql-mode buffer. This change also keeps
`sqlup-keywords' for now as they're necessary for caps-ing a region.


This **won't** work for use in org-mode or other major mode outside of `sql-mode` itself and its "products". sql-mode does set sql-mode-font-lock to be the correct keywords depending on the flavor. If the correct product is not set and changed after loading sql-mode, sqlup-mode must also be reloaded as it caches the regexes from whatever product font-lock sql-mode has when sqlUP-ing the first time.