If you have admin access to the koji pgsql DB...
I don't know if it's adapted to your koji db schema but I have found this: http://wiki.linux-kernel.at/index.php/Koji#Deleting_a_complete_package_from_the_database


2011/2/2 Josh Boyer <jwboyer@gmail.com>
On Tue, Feb 1, 2011 at 5:56 PM,  <steve.webb@beatport.com> wrote:
>> Remove a package in what sense? Can you give me an example of what you
>> want to accomplish?
> We used "add-pkg" to add a package using the full name i.e.
> blah-1.0.1-1.el5.yadda.yadda.yadda and we want to remove that because it
> was added by accident.  How do we do that?

I'm fairly sure that requires an admin to access and modify the
postgresql DB directly.  There are a number of checks in place before
you can delete it, but if they are met you should be able to delete
that row from the package table.