Replace eshell-defgroup with plain defgroup

Replace eshell-defgroup with plain defgroup

Borrowing a trick from vc-sccs.el, wrap the defgroup in a progn
so that the whole thing ends up in the generated autoload file,
esh-groups.el.

* em-alias.el, em-banner.el, em-basic.el, em-cmpl.el, em-dirs.el:
* em-glob.el, em-hist.el, em-ls.el, em-pred.el, em-prompt.el:
* em-rebind.el, em-script.el, em-smart.el, em-term.el, em-unix.el:
* em-xtra.el: Replace eshell-defgroup with (progn (defgroup.
* eshell.el (eshell-defgroup): Remove alias.