purescript-mode.el: remove unused purescript-completing-read-function

Author: Hi-Angel

purescript-mode.el

@@ -398,15 +398,6 @@ is asked to show extra info for the items matching QUERY.."
            current-prefix-arg)))
   (browse-url (format "https://pursuit.purescript.org/search?q=%s" query)))
 
-(defcustom purescript-completing-read-function 'completing-read
-  "Default function to use for completion."
-  :group 'purescript
-  :type '(choice
-          (function-item :tag "completing-read" :value completing-read)
-          (function-item :tag "ido" :value ido-completing-read)
-          (function-item :tag "helm" :value helm--completing-read-default)
-          (function :tag "Custom function")))
-
 (defcustom purescript-indent-spaces 2
   "Number of spaces to indent inwards."
   :type 'integer