pathephone: use `deprecate!` instead of `discontinued`

Casks/p/pathephone.rb

@@ -8,6 +8,8 @@ cask "pathephone" do
   desc "Distributed audio player"
   homepage "https://pathephone.github.io/"
 
+  deprecate! date: "2023-12-17", because: :discontinued
+
   auto_updates true
 
   app "Pathephone.app"
@@ -19,8 +21,4 @@ cask "pathephone" do
     "~/Library/Preferences/space.metabin.pathephone.plist",
     "~/Library/Saved Application State/space.metabin.pathephone.savedState",
   ]
-
-  caveats do
-    discontinued
-  end
 end