Include the major mode name in the `C-h b' output

Include the major mode name in the `C-h b' output

* lisp/calc/calc-help.el (calc-describe-bindings): Don't add the
name since it's there now.

* src/keymap.c (Fdescribe_buffer_bindings): Include the major mode
name for symmetry with the minor modes (and because it's easy to
forget).