Remove `groupclear` etc bindings

grep `groupclear` in the whole engine. There's default bindings but these don't actually do anything, the actual bind is `group unset`. This only serves to confuse people (for example https://springrts.com/phpbb/viewtopic.php?f=1&t=44462 and https://github.com/beyond-all-reason/Beyond-All-Reason/pull/1983 ). Part of the task is to check for other obsolete `groupfoo` binds and remove/replace them as well.

Start by grepping the whole engine for `groupclear`, then inspect the default bindings and compare them with the working `group unset` binding. Search for other obsolete `groupfoo` bindings, remove or replace them as appropriate, and consider the work done when no nonfunctional obsolete group bindings remain.

Written by the indexing model from the issue text.