shill: cellular: Remove mm1::ModemProxy::Driver.

Upstream ModemManager has replaced the 'Driver' property of the
org.freedesktop.ModemManager1.Modem interface with a 'Drivers' proeprty.
This CL removes mm1::ModemProxy::Driver to avoid incompatibility with
the generated DBus code.

BUG=chromium-os:33901
TEST=Build and run unit tests.

Change-Id: I5850015e3443ce0c21dd6fbfa7abe7305d59851d
Reviewed-on: https://gerrit.chromium.org/gerrit/31422
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
diff --git a/mm1_modem_proxy.cc b/mm1_modem_proxy.cc
index d600746..7dc3514 100644
--- a/mm1_modem_proxy.cc
+++ b/mm1_modem_proxy.cc
@@ -252,15 +252,6 @@
     return std::string();  // Make the compiler happy.
   }
 }
-const std::string ModemProxy::Driver() {
-  SLOG(DBus, 2) << __func__;
-  try {
-    return proxy_.Driver();
-  } catch (const DBus::Error &e) {
-    LOG(FATAL) << "DBus exception: " << e.name() << ": " << e.what();
-    return std::string();  // Make the compiler happy.
-  }
-}
 const std::string ModemProxy::Plugin() {
   SLOG(DBus, 2) << __func__;
   try {
diff --git a/mm1_modem_proxy.h b/mm1_modem_proxy.h
index 50d331e..b905abd 100644
--- a/mm1_modem_proxy.h
+++ b/mm1_modem_proxy.h
@@ -75,7 +75,6 @@
   virtual const std::string Revision();
   virtual const std::string DeviceIdentifier();
   virtual const std::string Device();
-  virtual const std::string Driver();
   virtual const std::string Plugin();
   virtual const std::string EquipmentIdentifier();
   virtual uint32_t UnlockRequired();
diff --git a/mm1_modem_proxy_interface.h b/mm1_modem_proxy_interface.h
index b1c4c16..ca213e4 100644
--- a/mm1_modem_proxy_interface.h
+++ b/mm1_modem_proxy_interface.h
@@ -79,7 +79,6 @@
   virtual const std::string Revision() = 0;
   virtual const std::string DeviceIdentifier() = 0;
   virtual const std::string Device() = 0;
-  virtual const std::string Driver() = 0;
   virtual const std::string Plugin() = 0;
   virtual const std::string EquipmentIdentifier() = 0;
   virtual uint32_t UnlockRequired() = 0;
diff --git a/mock_mm1_modem_proxy.h b/mock_mm1_modem_proxy.h
index 8e7a78e..0dc4dc4 100644
--- a/mock_mm1_modem_proxy.h
+++ b/mock_mm1_modem_proxy.h
@@ -71,7 +71,6 @@
   MOCK_METHOD0(Revision, const std::string());
   MOCK_METHOD0(DeviceIdentifier, const std::string());
   MOCK_METHOD0(Device, const std::string());
-  MOCK_METHOD0(Driver, const std::string());
   MOCK_METHOD0(Plugin, const std::string());
   MOCK_METHOD0(EquipmentIdentifier, const std::string());
   MOCK_METHOD0(UnlockRequired, uint32_t());