Use 'esh-module-autoload' for Eshell modules' defgroups

Use 'esh-module-autoload' for Eshell modules' defgroups

This will let modules define their own, regular autoloads, independent
of the core Eshell machinery for defining modules.

* lisp/eshell/em-alias.el (em-alias):
* lisp/eshell/em-banner.el (em-banner):
* lisp/eshell/em-basic.el (em-basic):
* lisp/eshell/em-cmpl.el (em-cmpl):
* lisp/eshell/em-dirs.el (em-dirs):
* lisp/eshell/em-elecslash.el (em-elecslash):
* lisp/eshell/em-extpipe.el:
* lisp/eshell/em-glob.el (em-glob):
* lisp/eshell/em-hist.el (em-hist):
* lisp/eshell/em-ls.el (em-ls):
* lisp/eshell/em-pred.el (em-pred):
* lisp/eshell/em-prompt.el (em-prompt):
* lisp/eshell/em-rebind.el (em-rebind):
* lisp/eshell/em-script.el (em-script):
* lisp/eshell/em-smart.el (em-smart):
* lisp/eshell/em-term.el (em-term):
* lisp/eshell/em-tramp.el (em-tramp):
* lisp/eshell/em-unix.el (em-unix):
* lisp/eshell/em-xtra.el (em-xtra): Use 'esh-module-autoload'.

* lisp/eshell/esh-module.el ("esh-module-loaddefs"): Load this instead
of "esh-groups".

* .gitignore: Change esh-groups.el to esh-module-loaddefs.el

(cherry picked from commit 4c924a53334035dc4089b24174012b54c020631b)