Removed the categorytable, mediatypetable, and subcategorytable
tables.  These three tables appear to be from an incomplete
patch from pre-git that defined these tables to implement
additional search limits, and are not present in the 2.2.9
package.  In 3.0, these tables did nothing - the only code that
referred to them are incomplete admin editors that lack HTML
templates and are not referred to anywhere.

The updatedatabase.pl logic to remove these tables is conservative;
the tables are dropped only if they exist and are all empty.  Effectively,
this means that they'll be dropped if you've been running a fresh install
of 3.0 from git or the alphas or betas; if you've upgraded your database
from 2.2.9, these tables likely weren't in your database to begin with.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>