Remove unused dependency

quickref.asd

 (asdf:defsystem quickref
   :author "Antoine Martin"
-  :depends-on (:quicklisp :alexandria :split-sequence :qlmapper)
+  :depends-on (:quicklisp :alexandria :qlmapper)
   :serial t
   :components ((:file "quickref")
 	       (:file "website")

quickref.lisp

 (defpackage quickref
-  (:use :cl :split-sequence)
+  (:use :cl)
   (:import-from :alexandria
    :starts-with-subseq)
   (:export :print-primary-systems