* debbugs: Use cl-lib. Use lexical-binding when available

* debbugs: Use cl-lib. Use lexical-binding when available

* debbugs-gnu.el: Only require subr-x at compile time.  Use cl-lib.
(debbugs-gnu-print-entry): Remove unused var `title-length'.
(debbugs-gnu-sort-title): Mark `s2' as unused.
* debbugs-org.el (debbugs-gnu): Use cl-lib.
* debbugs.el: Add `cl-lib' as dependency.  Use cl-lib.
(debbugs-soap-invoke-async): Mark `args' as unused.