Don't prepend module name for in-namespace fields of a non-root-level GoStruct & Deprecate GoStruct interface (#638)

* Don't prepend module name for in-namespace fields of a non-root-level GoStruct

For details see #637

Fixes #637

* Remove generated proto files

* re-add proto files

* Update ValidatedGoStruct and deprecate GoStruct

* Remove != nil check since method is nil tolerant

* Fully deprecate GoStruct

Author: wenovus

demo/bgp/testdata/bgp-ietf.json

@@ -1,11 +1,11 @@
 {
-   "openconfig-network-instance:global": {
+   "global": {
       "config": {
          "as": 15169,
          "router-id": "192.0.2.42"
       }
    },
-   "openconfig-network-instance:neighbors": {
+   "neighbors": {
       "neighbor": [
          {
             "config": {