[cleanup] Remove superfluous code after pip wheel

Now that we use `pip wheel` + `Wheel.install_as_egg` to produce
genuine eggs, we don't need to workaround the fact that we have
not-actually-egg `.egg` bundles anymore.

If we still do need to allow for non-eggs being installed in `~/.eggs`,
via extensions or others, we should revert this.
See https://github.com/buildout/buildout/pull/352

src/zc/buildout/easy_install.py

@@ -307,36 +307,15 @@ class Installer(object):
             self._versions = normalize_versions(versions)
 
     def _make_env(self):
-        full_path = self._get_dest_dist_paths() + self._path
-        env = pkg_resources.Environment(full_path)
-        # this needs to be called whenever self._env is modified (or we could
-        # make an Environment subclass):
-        self._eggify_env_dest_dists(env, self._dest)
-        return env
+        dest = self._dest
+        full_path = [] if dest is None else [dest]
+        full_path.extend(self._path)
+        return pkg_resources.Environment(full_path)
 
     def _env_rescan_dest(self):
-        self._env.scan(self._get_dest_dist_paths())
-        self._eggify_env_dest_dists(self._env, self._dest)
-
-    def _get_dest_dist_paths(self):
         dest = self._dest
-        if dest is None:
-            return []
-        eggs = glob.glob(os.path.join(dest, '*.egg'))
-        dists = [os.path.dirname(dist_info) for dist_info in
-                 glob.glob(os.path.join(dest, '*', '*.dist-info'))]
-        return list(set(eggs + dists))
-
-    @staticmethod
-    def _eggify_env_dest_dists(env, dest):
-        """
-        Make sure everything found under `dest` is seen as an egg, even if it's
-        some other kind of dist.
-        """
-        for project_name in env:
-            for dist in env[project_name]:
-                if os.path.dirname(dist.location) == dest:
-                    dist.precedence = pkg_resources.EGG_DIST
+        if dest is not None:
+            self._env.scan([dest])
 
     def _version_conflict_information(self, name):
         """Return textual requirements/constraint information for debug purposes