Refactor: libpacemaker, tools: Remove redundant stonith API cleanup code

stonith_api_delete() already performs a NULL-check, disconnects the
client, deletes notifications, etc. No need to explicitly do this before
calling it. It also is not worth functionizing
clean_up_fencing_connection() in crm_mon.c anymore.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>