Eliminated references to deprecated ONOS_NIC environment variable.

Change-Id: I9b709920c1aa2e7c1c4cb1f28f920dd2820b86ba
diff --git a/tools/dev/mininet/onos.py b/tools/dev/mininet/onos.py
index 6027180..f8e3703 100755
--- a/tools/dev/mininet/onos.py
+++ b/tools/dev/mininet/onos.py
@@ -111,7 +111,7 @@
 def updateNodeIPs( env, nodes ):
     "Update env dict and environ with node IPs"
     # Get rid of stale junk
-    for var in 'ONOS_NIC', 'ONOS_CELL', 'ONOS_INSTANCES':
+    for var in 'ONOS_CELL', 'ONOS_INSTANCES':
         env[ var ] = ''
     for var in environ.keys():
         if var.startswith( 'OC' ):