writefull: use deprecate! instead of discontinued

Casks/w/writefull.rb

@@ -8,6 +8,8 @@ cask "writefull" do
   desc "Provides feedback on your writing"
   homepage "https://writefullapp.com/"
 
+  deprecate! date: "2023-12-17", because: :discontinued
+
   app "Writefull.app"
 
   zap trash: [
@@ -18,8 +20,4 @@ cask "writefull" do
     "~/Library/Preferences/com.paraphrase.Writefull.plist",
     "~/Library/Saved Application State/com.paraphrase.Writefull.savedState",
   ]
-
-  caveats do
-    discontinued
-  end
 end