DEC threads: Simplify updating the thread list

DEC threads: Simplify updating the thread list

Seems to me that we can simplify DEC thread's
target_update_thread_list implementation, avoiding the need to build
the array of GDB threads.

I have no way to test this, but then again support for Tru64 is about
to be removed.

Pushing anyway to have the last version in git be the cleanest one
should start from, if this file turns out to be resurrected in the
future.

gdb/
2014-10-15  Pedro Alves  <palves@redhat.com>

	* dec-thread.c (dec_thread_count_gdb_threads)
	(dec_thread_add_gdb_thread): Delete.
	(dec_thread_update_thread_list): Delete.
	(dec_thread_find_new_threads): Rename to ...
	(dec_thread_update_thread_list): ... this.  Delete GDB-size
	threads that are no longer found in dec_thread_list.
	(resync_thread_list): Delete.
	(dec_thread_wait): Call dec_thread_update_thread_list instead of
	resync_thread_list.