cashew: remove GetConnectivityState from ServiceManagerMock

The CL for issue 3281 removed the GetConnectivityState method from the
ServiceManager class, but did not remove it from the mock for that
class. Fix this so that unit tests will build.

BUG=chromium-os:3281
TEST=FEATURES=test emerge-${BOARD} cashew

Change-Id: I4148f22f4e1f9d02990757feb1b7002c14a0f301
Reviewed-on: http://gerrit.chromium.org/gerrit/1834
Tested-by: Vince Laviano <vlaviano@chromium.org>
Reviewed-by: Jason Glasgow <jglasgow@chromium.org>