netbox: remove schema_version from requests

Schema_version was used in netbox to update local box-like
schema. The box-like schema makes able to access spaces and
indexes via connection object.

It was updated each time, when a response from a server is
received with a schema version non-equal to the local value.

But there was no reason why a schema version is needed in a
request. It leads to ER_WRONG_SCHEMA_VERSION error sometimes,
but netbox on this error just resends the same request again. The
same behaviour can be reached with just no sending any schema
version to a server.

Remove schema_version from request, and just track schema version
changes in responses.

Part of #3351
Part of #3333
Follow up #3107