lang/haskell: remove intero support

The package was deprecated and abandoned upstream since November 2019.

Closes #2121

modules/lang/haskell/autoload.el

@@ -4,12 +4,9 @@
 (defun +haskell/open-repl (&optional arg)
   "Opens a Haskell REPL."
   (interactive "P")
-  (if-let*
-      ((window
-        (display-buffer
-         (if (featurep! +intero)
-             (intero-repl-buffer arg)
-           (haskell-session-interactive-buffer (haskell-session))))))
+  (if-let (window
+           (display-buffer
+            (haskell-session-interactive-buffer (haskell-session))))
       (window-buffer window)
     (error "Failed to display Haskell REPL")))