Prefer the defcustom :risky property in eshell

Prefer the defcustom :risky property in eshell

* lisp/eshell/em-banner.el (eshell-banner-message):
* lisp/eshell/em-hist.el (eshell-input-filter):
* lisp/eshell/em-pred.el (eshell-predicate-alist)
(eshell-modifier-alist):
* lisp/eshell/esh-cmd.el (eshell-subcommand-bindings):
* lisp/eshell/esh-io.el (eshell-virtual-targets):
* lisp/eshell/esh-var.el (eshell-variable-aliases-list): Prefer
defcustom :risky property to setting 'risky-local-variable manually.