Revert "Start to hard depend on slapos.libnetworkcache."

As slapos.libnetworkcache development shall be outside on buildout, do not
create hard dependency.

This reverts commit 4dc2aef8.

networkcached.cfg

-# In order to use this profile it is required to either clone in zc.buildout
-# directory slapos.libnetworkcache or fix develop target.
 [buildout]
 extends = buildout.cfg
 
 parts += nc pync testnc
-develop += slapos.libnetworkcache
 
 [nc]
 recipe = z3c.recipe.scripts