The do_nothing function in mi-main.c is used as a splay tree
key-deleting function; but NULL serves the same purpose and is used
elsewhere in gdb. This patch removes the unneeded function.
ChangeLog
2017-10-09 Tom Tromey <tom@tromey.com>
* mi/mi-main.c (do_nothing): Remove.
(list_available_thread_groups): Update.