Eliminate TUnixDgSocketWriter.  Use TBruceClientSocket instead.

	modified:   src/bruce/bruce.test.cc
	modified:   src/bruce/input_thread.test.cc
	modified:   src/bruce/simple_client/simple_bruce_client.cc
	modified:   src/bruce/test_util/misc_util.h
	deleted:    src/bruce/test_util/unix_dg_socket_writer.cc
	deleted:    src/bruce/test_util/unix_dg_socket_writer.h