Remove duplicate Lisp definitions of define-minor-mode variables defined in C.

Remove duplicate Lisp definitions of define-minor-mode variables defined in C.

* lisp/abbrev.el (abbrev-mode):
* lisp/composite.el (auto-composition-mode):
* lisp/menu-bar.el (menu-bar-mode):
* lisp/simple.el (transient-mark-mode):
* lisp/tool-bar.el (tool-bar-mode): Adjust the define-minor-mode calls so
that they do not define the associated variables twice.
* lisp/simple.el (transient-mark-mode): Remove defvar.
* lisp/composite.el (auto-composition-mode): Make variable auto-buffer-local.
* lisp/cus-start.el: Add transient-mark-mode, menu-bar-mode, tool-bar-mode.
Handle multiple groups, and also custom-delayed-init-variables.
* lisp/emacs-lisp/easy-mmode.el (define-minor-mode): Doc fix.

* src/buffer.c (syms_of_buffer) <abbrev-mode, transient-mark-mode>:
* src/frame.c (syms_of_frame) <tool-bar-mode>: Move docs here from Lisp.