Remove connection-string elements from attributes

[JatinSanghvi]

Current extension supports both RabbitMQ connection URI e.g. amqp://user:pass@host:10000/vhost and individual connection-string elements (user, pass, host, and 1000) to be specified in trigger and output bindings. With the latter way to specify connection information, some of the elements were still missing, namely isSslEnabled and vHost. We recently added commit to include attribute property for isSslEnabled. Instead of adding and maintaining these many number of attribute properties, this commit removes the latter support. This would also eliminate combinations like hostname coming from appsettings but port coming from attributes, which is not what we expect from users.

As per my research, most of the users use connection strings in their functions. Since next one would be a version 2.x release, I am taking the opportunity to introduce this breaking change. Users using connection strings already are not expected to update their functions to upgrade to v2.x release. The other WebJobs extensions from Azure only support connection strings, as far as I have seen.

[v-shenoy]

Nice work, @JatinSanghvi.
The changes look thorough.