IDENTITY_API_VERSION is hardcoded to 3 in most locations already, drop
the remaining occurrences, but keep the variable definition since some
plugins still depend on it. Drop ENABLE_IDENTITY_V2 which no longer
has any effect.
Amend variable list for bootstrap_keystone().
Signed-off-by: Dr. Jens Harbott <harbott@osism.tech>
Change-Id: I06f476d2105bc6ec2b511fc5effcfcc3973eaf97