Make bindings--define-key obsolete

Make bindings--define-key obsolete

It used to be like 'define-key', but was used for making pure copies of
as much of a menu's data as possible.  With purespace now gone, it can
be replaced by 'define-key'.

* lisp/bindings.el (bindings--define-key): Make into obsolete
alias for 'define-key'.  Update all callers.

(cherry picked from commit 1de87314c4c3cd01526e31bb805e2857fe749485)