Revert dgm config to keep the correct baseline

Change-Id: Ib93405c0bbb05e820cbead05b58ae2a06b9711aa
Reviewed-on: https://review.couchbase.org/c/perfrunner/+/168038
Tested-by: Build Bot <[email protected]>
Reviewed-by: vikas chaudhary <[email protected]>

Author: vikas-getconnect

tests/gsi/plasma/config/config_scanthr_dgm_plasma.json

@@ -17,9 +17,7 @@
             "Inclusion": 3,
             "Index": "myindex",
             "NInterval": 100,
-            "TestSpec": {
-                "RandomKeyLen": 12
-            }
+            "RandomLen" : 12
         }
     ]
 }