Remove Block Storage API v2 support

The Block Storage API v2 was deprecated in Pike by change
I913c44799cddc37c3342729ec0ef34068db5b2d4 and is (finally)
being removed in Xena [0].  So remove v2 support from devstack.

[0] https://wiki.openstack.org/wiki/CinderXenaPTGSummary#Removing_the_Block_Storage_API_v2

Depends-on: https://review.opendev.org/c/openstack/devstack/+/792048
Change-Id: I856d78648d28ac4cad0fb212bef1ae6ad32fca90
2 files changed