futures: get rid of extend_path
This is used so mutliple directories can provide a package. We don't
need it when vendoring.
Differential Revision: https://phab.mercurial-scm.org/D3262
--- a/mercurial/thirdparty/concurrent/__init__.py Wed Apr 11 14:48:24 2018 -0700
+++ b/mercurial/thirdparty/concurrent/__init__.py Mon Apr 09 12:19:37 2018 -0700
@@ -1,3 +0,0 @@
-from pkgutil import extend_path
-
-__path__ = extend_path(__path__, __name__)