Nix some useless uses of looking-at, looking-back

Nix some useless uses of looking-at, looking-back

* lisp/allout.el (allout-kill-topic):
(allout-next-topic-pending-encryption):
* lisp/bookmark.el (bookmark-kill-line):
* lisp/cus-edit.el (custom-save-variables, custom-save-faces):
* lisp/cus-theme.el (custom-theme-write-variables):
(custom-theme-write-faces):
* lisp/emacs-lisp/autoload.el (autoload-generate-file-autoloads):
* lisp/emacs-lisp/bytecomp.el (byte-compile-from-buffer):
* lisp/emacs-lisp/checkdoc.el (checkdoc-interactive-loop):
(checkdoc-interactive-ispell-loop):
(checkdoc-message-interactive-ispell-loop, checkdoc-this-string-valid):
(checkdoc-this-string-valid-engine):
* lisp/emacs-lisp/elint.el (elint-get-top-forms):
* lisp/emulation/viper-cmd.el (viper-backward-indent):
* lisp/image-dired.el (image-dired-delete-char):
* lisp/simple.el (kill-visual-line): Replace instances of looking-at,
looking-back with char comparisons using following-char, preceding-char.