Revert "Merge pull request #28283 from y-yagi/silence_puma_startup_messages_in_system_test"

This reverts commit 0d73f911, reversing
changes made to 21ff8a49.

We don't want to silence Puma because it's start up messages can be
useful (to see threads, port etc). #28109 was instead fixed by not
running system tests by defaul with `bin/rails test` in #28286.

actionpack/lib/action_dispatch/system_testing/server.rb

@@ -11,7 +11,7 @@ def run
       private
         def register
           Capybara.register_server :rails_puma do |app, port, host|
-            Rack::Handler::Puma.run(app, Port: port, Threads: "0:1", Silent: true)
+            Rack::Handler::Puma.run(app, Port: port, Threads: "0:1")
           end
         end