classifier: Fix theoretical leak in classifier_destroy().

classifier: Fix theoretical leak in classifier_destroy().

The open-coded version of destroy_table() in classifier_destroy() didn't
free the table's minimatch.  Use destroy_table() to do it properly.

This is only a theoretical leak because all the existing callers actually
remove all the rules from their classifiers before they destroy them
(outside of the tests/ directory, which I didn't examine) and so they don't
ever have anything left to remove in classifier_destroy().

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>