Remove duplicate six http_archive definition

Archive is declared in the protobuf_deps() call above

WORKSPACE

@@ -16,13 +16,6 @@ load("//:protobuf_deps.bzl", "protobuf_deps")
 # Load common dependencies.
 protobuf_deps()
 
-http_archive(
-    name = "six",
-    build_file = "@//:third_party/six.BUILD",
-    sha256 = "d16a0141ec1a18405cd4ce8b4613101da75da0e9a7aec5bdd4fa804d0e0eba73",
-    urls = ["https://pypi.python.org/packages/source/s/six/six-1.12.0.tar.gz"],
-)
-
 bind(
     name = "python_headers",
     actual = "//util/python:python_headers",