Remove HyperVNeutronPlugin

Remove HyperVNeutronPlugin

HyperVNeutronPlugin is hereby removed, as it is outdated
and it is no longer needed, thanks to Ml2Plugin. All of its
users should switch to Ml2Plugin.

The database tables 'hyperv_vlan_allocations' and
'hyperv_network_bindings' will no longer be used, since their
consumer will be removed.

Adds database migration script which will move all the existent
entries in the mentioned tables to their Ml2 equivalent ones.

Partially-implements: blueprint core-vendor-decomposition

Change-Id: If02c4761d9653dcd81fc0043ecce86a3b149dd99