Remove default keyword

I just stumbled upon a code in PS `routing-duplex`, where `default` is
a function name and it's getting highlighted. That made me dig to see
where such keyword could be used to reduce the possibility of such
false-positives.

Now, I personally don't remember `default` being ever used as a
keyword in PS. So I asked an AI but it doesn't know either. Then as a
last measure I looked at syntax highlight in VS Code editor, and they
don't highlight `default` either.

So remove `default` from the list of keywords.

Author: Hi-Angel

purescript-font-lock.el

@@ -178,7 +178,7 @@ Returns keywords suitable for `font-lock-keywords'."
           ;; spec syntax, but they are not reserved.
           ;; `_' can go in here since it has temporary word syntax.
           (regexp-opt
-           '("ado" "case" "class" "data" "default" "deriving"
+           '("ado" "case" "class" "data" "deriving"
              "do" "else" "if" "import" "in" "infix" "infixl"
              "infixr" "instance" "let" "module" "newtype" "of"
              "then" "type" "where" "_") 'words))