There are two implementation code for similar API in Nova repository.
One is newer: v2.1 API, another is legacy: v2 API. v2.1 API has been
used as the default API since Liberty and legacy v2 API has been marked
as deprecated. We have used and tested v2.1 API so well and now is
nice time to remove legacy API code based on the consensus of the
design summit of Austin.
This patch removes NOVA_V2_LEGACY which set up legacy API code.
NOTE: The gate job which uses this NOVA_V2_LEGACY option has been
removed already since Iac81b7d569b76b99e9d86eaa5001ae7f9b78cdfe.
Partially implements blueprint remove-legacy-v2-api-code
Change-Id: I0e16b7ce608d7eeb3a35fd77e66531dfc8c142ef