Remove special_fields definition

Since volume v1 test has been removed from Tempest, then
the difference of field name and description between v1 and v2
no longer exists, so we no longer need the special_fields
definition, this is to remove them for the code clean.

Change-Id: I82ba0607dda5a8a4b4badd406862dbfc02fbe7d3
8 files changed