Remove unused RFCViolation

This is to remove unused RFCViolation exception.

Change-Id: Id1c4f421ca47ff075d2df236fe302565fcaa57ea
diff --git a/tempest/exceptions.py b/tempest/exceptions.py
index a8a6ff0..a430d5d 100644
--- a/tempest/exceptions.py
+++ b/tempest/exceptions.py
@@ -52,9 +52,5 @@
                "the configured network")
 
 
-class RFCViolation(exceptions.RestClientException):
-    message = "RFC Violation"
-
-
 class InvalidServiceTag(exceptions.TempestException):
     message = "Invalid service tag"