[EventHubs] remove unused packages in the dev_requirement
The three packages specified in dev requirement are not used in azure-eventhub v5 anymore.
I believe those are carried over from the track1: and could be removed from the dev requirements in v5.
```
docutils>=0.14
pygments>=2.2.0
behave==1.2.6
```
-e ../azure-mgmt-eventhub
-e ../../resources/azure-mgmt-resource
aiohttp>=3.0; python_version >= '3.5'
-docutils>=0.14
-pygments>=2.2.0
-behave==1.2.6
-e ../../../tools/azure-devtools
\ No newline at end of file
