Revert "Allow to find slapos.libnetworkcache during test."

Doing development of zc.buildout parts which shall depend on
slapos.libnetworkcache without ability to develop it locally is nowhere path.

This reverts commit bacd2505.

src/zc/buildout/testing.py

@@ -269,7 +269,7 @@ def make_buildout(executable=None):
     """Make a buildout that uses this version of zc.buildout."""
     # Create a basic buildout.cfg to avoid a warning from buildout.
     open('buildout.cfg', 'w').write(
-        "[buildout]\nparts =\nfind-links = http://pypi.python.org/pypi/slapos.libnetworkcache"
+        "[buildout]\nparts =\n"
         )
     # Get state of installer defaults so we can reinstate them (instantiating
     # a Buildout will force the Buildout's defaults on the installer).