[Service Bus] Remove dead letter info from PeekedMessage

[ramya-rao-a]

In version 7.0.0-b7 of the Azure Service Bus package, we have the peek method on receivers returning an array of PeekedMessage. This has the below properties that are available on dead lettered messages:

• property dead_letter_error_description: Optional[str] # Read-only
• property dead_letter_reason: Optional[str] # Read-only
• property dead_letter_source: Optional[str] # Read-only

It is not clear if peeked messages on the dead letter queue will even have these properties.

I would recommend we remove these properties for now, do the right testing in the future and add these back if we see that they apply