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

test/cli/prune_test.rb

@@ -10,7 +10,7 @@ class CliPruneTest < CliTestCase
 
   test "images" do
     run_command("images").tap do |output|
-      assert_match "docker image prune --force --filter label=service=app --filter dangling=true on 1.1.1.", output
+      assert_match "docker image prune --force --filter label=service=app on 1.1.1.", output
       assert_match "docker image ls --filter label=service=app --format '{{.ID}} {{.Repository}}:{{.Tag}}' | grep -v -w \"$(docker container ls -a --format '{{.Image}}\\|' --filter label=service=app | tr -d '\\n')dhh/app:latest\\|dhh/app:<none>\" | while read image tag; do docker rmi $tag; done on 1.1.1.", output
     end
   end