purescript-mode.el: remove warning about purescript-font-lock-symbols

It's been there since 2019 and the variable has been no-op since then
as well. I think it's fair to assume anyone who were still using the
variable either moved on, or if they didn't notice anything, they will
probably keep not noticing anything, because the variable has been
no-op for so long.

Author: Hi-Angel

purescript-mode.el

@@ -325,10 +325,7 @@ see documentation for that variable for more details."
   (setq-local beginning-of-defun-function 'purescript-beginning-of-defun)
   (setq prettify-symbols-alist purescript-font-lock-prettify-symbols-alist
         ;; make (ff-find-other-file) find .js FFI file, given .purs
-        ff-other-file-alist '((".purs\\'" (".js"))))
-  (when (bound-and-true-p purescript-font-lock-symbols)
-    (warn "`purescript-font-lock-symbols' is obsolete: please enable `prettify-symbols-mode' locally or globally instead."))
-  )
+        ff-other-file-alist '((".purs\\'" (".js")))))
 
 (defun purescript-fill-paragraph (justify)
   (save-excursion