Prefer defcustom :local specifier in allout

Prefer defcustom :local specifier in allout

* lisp/allout-widgets.el (allout-widgets-track-decoration):
* lisp/allout.el (allout-inhibit-auto-fill)
(allout-inhibit-auto-fill-on-headline, allout-use-hanging-indents)
(allout-reindent-bodies, allout-show-bodies, allout-header-prefix)
(allout-primary-bullet, allout-plain-bullets-string)
(allout-distinctive-bullets-string, allout-old-style-prefixes)
(allout-stylish-prefixes, allout-numbered-bullet)
(allout-presentation-padding, allout-encrypt-unencrypted-on-saves)
(allout-enable-file-variable-adjustment): Prefer defcustom :local
specifier to using 'make-variable-buffer-local' directly.

(cherry picked from commit df8d8a786f10de780235618cdf9af7fbc139620c)