Remove Emacs 21 stuff.

Remove Emacs 21 stuff.

mm-util.el (mm-codepage-iso-8859-list, mm-charset-eval-alist, mm-mime-charset): Comment fix.
rfc2047.el (rfc2047-syntax-table): Comment fix.
utf7.el (utf7-utf-16-coding-system): Comment fix.
nnrss.el (nnrss-read-server-data, nnrss-read-group-data): Use `load' rather than `insert-file-contents' and `eval-region'.
pgg.el (pgg-run-at-time-1): Define it for XEmacs only; fix if/else construction.
time-date.el: No need to require cl for Emacs 21.