Remove redundant XCMs from dry run's forwarded xcms

[franciscoaguirre]

Description

This PR addresses #5878.

After dry running an xcm on asset hub, we had redundant xcms showing up in the forwarded_xcms field of the dry run effects returned.
These were caused by two things:

• The UpwardMessageSender router always added an element even if there were no messages.
• The two routers on asset hub westend related to bridging (to rococo and sepolia) getting the message from their queues when their queues is actually the same xcmp queue that was already contemplated.

In order to fix this, we check for no messages in UMP and clear the implementation of InspectMessageQueues for these bridging routers.
Keep in mind that the bridged message is still sent, as normal via the xcmp-queue to Bridge Hub.
To keep on dry-running the journey of the message, the next hop to dry-run is Bridge Hub.
That'll be tackled in a different PR.

TODO

• Functionality
• Test