(require :cl-ppcre)
(defun remove-comment (str)
  (ppcre:regex-replace-all "/\\*(.+?)(\\*/|$)" str ""))

(remove-comment "AAA")                  ; => "AAA"
(remove-comment "AAA/*BBB*/")           ; => "AAA"
(remove-comment "AAA/*BBB")             ; => "AAA"
(remove-comment "AAA/*BBB*/CCC")        ; => "AAACCC"
(remove-comment "AAA/*BBB/*CCC*/DDD*/EEE") ; => "AAADDD*/EEE"
(remove-comment "AAA/a//*BB*B**/CCC")      ; => "AAA/a/CCC"