filectx: remove __new__

filectx: remove __new__

It does not seem to be used anywhere, and breaks a later patch.

--- a/mercurial/context.py	Tue May 09 16:34:12 2017 -0700
+++ b/mercurial/context.py	Tue May 09 19:16:48 2017 -0700
@@ -688,9 +688,6 @@
     workingfilectx: a filecontext that represents files from the working
                     directory,
     memfilectx: a filecontext that represents files in-memory."""
-    def __new__(cls, repo, path, *args, **kwargs):
-        return super(basefilectx, cls).__new__(cls)
-
     @propertycache
     def _filelog(self):
         return self._repo.file(self._path)