Remove XEmacs compat code from allout.el
* lisp/allout.el (allout-overlay-preparations) (allout-overlay-interior-modification-handler) (allout-before-change-handler, allout-beginning-of-line) (allout-solicit-alternate-bullet, allout-annotate-hidden) (allout-hide-by-annotation, allout-yank-processing) (allout-flag-region, allout-toggle-subtree-encryption) (allout-mark-marker, allout-substring-no-properties) (allout-select-safe-coding-system) (allout-previous-single-char-property-change) (allout-next-single-char-property-change) (top-level): Remove XEmacs compat code.