Remove new_thread_notify and dead_thread_notify

Remove new_thread_notify and dead_thread_notify

They were added by

  PATCH: Multithreaded debugging for gdbserver
  https://sourceware.org/ml/gdb-patches/2002-06/msg00157.html

but as a no-op, and the last usage of them was removed by

  [gdbserver/RFC/RFA] Implement multiprocess extensions, add linux multiproces support.
  https://sourceware.org/ml/gdb-patches/2009-03/msg00667.html

This patch is to remove them.

gdb/gdbserver:

2016-01-25  Yao Qi  <yao.qi@linaro.org>

	* remote-utils.c (new_thread_notify): Remove.
	(dead_thread_notify): Likewise.
	* remote-utils.h (new_thread_notify): Remove declaration.
	(dead_thread_notify): Likewise.