Remove unused net_profile_docker_bridge_cidr (#222)

Since 2020 the default runtime is containerd and not Docker
https://github.com/Azure/AKS/blob/master/CHANGELOG.md#release-2020-06-29

The setting docker_bridge_cidr is doing nothing.
If you check the interfaces on the AKS nodes they dont have any Docker bridge configured.

Related: hashicorp/terraform-provider-azurerm#18119