Remove some compat code for old versions and XEmacs

Remove some compat code for old versions and XEmacs

* lisp/ibuf-ext.el (ibuffer-old-saved-filters-warning)
(ibuffer-maybe-save-stuff): Assume customize-save-variable is
bound; it is autoloaded.
* lisp/cedet/semantic/symref/grep.el (semantic-symref-perform-search):
* lisp/password-cache.el (password-cache-remove):
* lisp/cedet/semantic/bovine/el.el (semantic-dependency-tag-file):
Remove Emacs 21 compat code.
* lisp/cedet/semantic/sort.el (semantic-string-lessp-ci):
Remove Emacs 20 compat code.
* test/lisp/cedet/semantic-utest.el (semantic-utest-temp-directory):
* lisp/mail/supercite.el (sc-ask): Remove XEmacs compat code.
* lisp/progmodes/idlw-shell.el (idlwave-shell-mode):
* lisp/progmodes/idlwave.el (idlwave-mode): Remove commented out
compat code.