Remove delivery_mode header from AMQP 1.0 Shovel

[luos]

This header is not present if delivery_mode = 2, it does not really makes sense to leave it when delivery_mode = 1.
The durability of the message is reflected in the durable flag of the amqp 1.0 message.

Let me know what you think.

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[michaelklishin]

@luos why wasn't this submitted against main?

[luos]

Hi, I've made the PR into 3.12.x because it is a follow up of #10037.

It can be submitted to main as well, I will do that.

[luos]

Moved to #10510