Restore the ERR_remove_thread_state() API and make it a no-op

The ERR_remove_thread_state() API is restored to take a pointer
argument, but does nothing more.  ERR_remove_state() is also made into
a no-op.  Both functions are deprecated and users are recommended to
use OPENSSL_thread_stop() instead.

Documentation is changed to reflect this.

Reviewed-by: Matt Caswell <matt@openssl.org>