Eliminate last uses of 'cl' in lisp/mail/

Eliminate last uses of 'cl' in lisp/mail/

* lisp/mail/binhex.el: Use lexical-binding and avoid cl.
(binhex-push-char): Remove unused arg 'count'.
(binhex-decode-region-external): Remove unused var 'status'.

* lisp/mail/flow-fill.el: Use lexical-binding and avoid cl.

* lisp/mail/footnote.el: Reduce redundancy.
(footnote-roman-lower-regexp, footnote-roman-upper-regexp)
(footnote-roman-upper-list): Auto-generate from footnote-roman-lower-list.
(footnote-hebrew-numeric-regex): Auto-generate from footnote-hebrew-numeric.
(footnote--hebrew-numeric): Simplify.
(footnote-hebrew-symbolic-regex): Generate from footnote-hebrew-symbolic.

* lisp/mail/hashcash.el: Use lexical-binding and avoid cl.
(hashcash-verify-payment): Use pcase.

* lisp/mail/ietf-drums.el: Use lexical-binding and avoid cl.
(ietf-drums-token-to-list): Remove unused var 'e'.

* lisp/mail/rfc2231.el: Use lexical-binding and avoid cl.

* lisp/mail/uudecode.el: Use lexical-binding and avoid cl.
(uudecode-char-int): Remove unused 'eval-and-compile' wrapper.
(uudecode-decode-region-external): Remove unused 'status' var.
(uudecode-string-to-multibyte): Remove.
(uudecode-decode-region-internal): Use decode-coding-string instead.

* lisp/mail/yenc.el: Use lexical-binding and avoid cl.