Use egg.mk, not distutils.mk.

This package can use either setuptools (egg.mk) or distutils
(distutils.mk), but it prefers setuptools and thus should be built
with our egg.mk support.  Adjust PLIST for egg.mk (different)
variables and drop eggfile conditionalization, as eggs always have
egg-info directories.

Thanks to dholland@ and obache@ for noticing/suggesting.

(gdt)