How to remove erroneous deps from pkgng

[Reko Turja]

I'm testing out the pkgng system and somehow a port managed to pull 
devel/pkg-config into one low level port polluting whole db. "pkg check" 
just wants to install the annoying thing. Is there any way to get rid of 
that erroneous dependency?

In production system, these kind of errors should be somehow correctable, 
especially if pkgng is to be used with ports as well.

-Reko