The use of the ravenscar_open static global is unnecessary.
This patch removes it. It also removes some routines that
were created in association with the management of this global.
gdb/ChangeLog:
* ravenscar-thread.c (ravenscar_is_open): Delete.
(ravenscar_initialize): Move most of the code from here...
(ravenscar_inferior_created): ... to there. Invert logic.
(ravenscar_close): Delete.
(init_ravenscar_thread_ops): Remove setting of
ravenscar_ops.to_close.