purescript-indent.el: make purescript-indent-mode truly buffer-local

It was defined with `defvar` and then made into buffer-local
with (make-variable-buffer-local). The call though was only executed
once, which is likely an omission.

Fix that and make it truly buffer-local.

Author: Hi-Angel

purescript-indent.el

@@ -1486,9 +1486,8 @@ One indentation cycle is used."
 
 ;;; purescript-indent-mode
 
-(defvar purescript-indent-mode nil
+(defvar-local purescript-indent-mode nil
   "Non-nil if the semi-intelligent PureScript indentation mode is in effect.")
-(make-variable-buffer-local 'purescript-indent-mode)
 
 (defvar purescript-indent-map
   (let ((map (make-sparse-keymap)))