Event Hub library version is declared in AMQP package

[srnagar]

Move the library version constant to Event Hubs library. It's currently in AMQP library.

https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/core/azure-core-amqp/src/main/java/com/azure/core/amqp/implementation/ClientConstants.java#L10

[sima-zhu]

One more action item for the issue is to remove hard-coded version as described in #6557