decouple buck yang plugin from buck main archive

- prep to allow bumping yang tool versin without releasing whole
  onos-buck archive

- with this patch,
  reverting back from locally patched state
  (= undo `patch-yang-libs`)
  will be:
   $ git checkout -- lib/BUCK tools/build/onos-buck

Change-Id: I06bfccdcfd6b22e2252b5c9dc145cece26058841
diff --git a/lib/deps.json b/lib/deps.json
index 6233aac..cb9300c 100644
--- a/lib/deps.json
+++ b/lib/deps.json
@@ -247,7 +247,7 @@
     "aries-util": "mvn:org.apache.aries:org.apache.aries.util:1.1.1",
     "guava20": "mvn:com.google.guava:guava:20.0",
 
-    // Note: update BVER in tools/dev/bin/patch-yang-libs
+    // Note update BVER in tools/dev/bin/patch-yang-libs and YANG_VER in tools/build/onos-buck
     "onos-yang-model":"mvn:org.onosproject:onos-yang-model:2.4",
     "onos-yang-compiler-api":"mvn:org.onosproject:onos-yang-compiler-api:2.4",
     "onos-yang-runtime":"mvn:org.onosproject:onos-yang-runtime:2.4",