'local_as' no longer depends on bgp.session

[jbemmel]

The example at https://github.com/ipspace/netlab/blob/dev/docs/plugins/ebgp.multihop.md#integration-with-other-bgp-plugins may be dated?

IIRC local_as used to be part of bgp.utils, but was moved to the core module. It is no longer required