ghc-nokinds: remove "nokinds" tag from derivation name

The name of the GHC derivation must match the name and version tuple GHC
uses to identify itself, because the withPackages wrapper uses that name
to construct installation library paths etc., and those paths must match
those constructed by the compiler. If we add another tag to the name
that GHC itself doesn't use, then the paths assumed to exist by the
wrapper are wrong.