shill: use ControlInterface to create proxy objects

So that appropriate proxy objects can be created based on the type of
the control interface.

While there, remove ProxyFactory related files.

BUG=chromium:513791
TEST=USE="asan clang cellular wimax dhcpv6" FEATURES=test emerge-$BOARD shill

Change-Id: I465b0807ab4ccacac3891638db41384f43ef83c5
Reviewed-on: https://chromium-review.googlesource.com/289855
Reviewed-by: Zeping Qiu <zqiu@chromium.org>
Commit-Queue: Zeping Qiu <zqiu@chromium.org>
Tested-by: Zeping Qiu <zqiu@chromium.org>
diff --git a/cellular/mock_cellular.h b/cellular/mock_cellular.h
index b5a517d..8ebe4ae 100644
--- a/cellular/mock_cellular.h
+++ b/cellular/mock_cellular.h
@@ -23,8 +23,7 @@
                Type type,
                const std::string& owner,
                const std::string& service,
-               const std::string& path,
-               ProxyFactory* proxy_factory);
+               const std::string& path);
   ~MockCellular() override;
 
   MOCK_METHOD1(Connect, void(Error* error));