AETHER-3189 Update ids to be dns compliant:

Change-Id: Ic03b51c62fb205a5505a15e743f93b0057f9b93b
diff --git a/config-models/aether-2.0.x/files/yang/onf-slice.yang b/config-models/aether-2.0.x/files/yang/onf-slice.yang
index f59619a..cad763f 100755
--- a/config-models/aether-2.0.x/files/yang/onf-slice.yang
+++ b/config-models/aether-2.0.x/files/yang/onf-slice.yang
@@ -5,7 +5,6 @@
 submodule onf-slice {
   belongs-to onf-enterprise { prefix ent; }
 
-  import ietf-yang-types{ prefix yg; }
   import onf-aether-types{ prefix at; }
 
   include onf-upf;
@@ -30,9 +29,7 @@
   }
 
   typedef slice-id {
-        type yg:yang-identifier {
-            length 1..32;
-        }
+    type at:aether-identifier;
     description "The typedef for slice-id";
   }