Remove the dangling=true filter

This has been removed from Docker Engine 24 and `docker image prune`
only deletes dangling images anyway.

Fixes https://github.com/basecamp/kamal/issues/410

lib/kamal/cli/prune.rb

@@ -7,7 +7,7 @@ class Kamal::Cli::Prune < Kamal::Cli::Base
     end
   end
 
-  desc "images", "Prune dangling images"
+  desc "images", "Prune unused images"
   def images
     mutating do
       on(KAMAL.hosts) do

lib/kamal/commands/prune.rb

@@ -3,7 +3,7 @@ require "active_support/core_ext/numeric/time"
 
 class Kamal::Commands::Prune < Kamal::Commands::Base
   def dangling_images
-    docker :image, :prune, "--force", "--filter", "label=service=#{config.service}", "--filter", "dangling=true"
+    docker :image, :prune, "--force", "--filter", "label=service=#{config.service}"
   end
 
   def tagged_images