FIX: allows listing messages of any thread (#27259)

Before this fix we could only list messages of a thread if it was part of a `threading_enabled` channel or if the thread was set to `force`.

Due to our design of also using a thread id when this is just a chain of replies so we can switch from threading enabled to disabled at any time, we will allow `Chat:: ListChannelThreadMessages` to list the messages of any thread, the only important requirements are:
- having a thread id
- being able to access this thread

To allow this, this commit simply removes the check on `threading_enabled` or `force`.

plugins/chat/lib/chat_sdk/thread.rb

@@ -86,9 +86,6 @@ module ChatSDK
         on_success { result.messages }
         on_failed_policy(:can_view_thread) { raise "Guardian can't view thread" }
         on_failed_policy(:target_message_exists) { raise "Target message doesn't exist" }
-        on_failed_policy(:ensure_thread_enabled) do
-          raise "Threading is not enabled for this channel"
-        end
         on_failure { raise "Unexpected error" }
       end
     end