Convert RegistrarServlet to RegistrarAction

Convert to an action and remove ResourceServlet, JsonTransportServlet and
JsonTransportServlet, all of which exist only to support it.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=137519385

java/google/registry/request/JsonActionRunner.java

@@ -35,9 +35,13 @@ public final class JsonActionRunner {
     Map<String, ?> handleJsonRequest(Map<String, ?> json);
   }
 
-  @Inject @JsonPayload Map<String, Object> payload;
-  @Inject JsonResponse response;
-  @Inject JsonActionRunner() {}
+  @JsonPayload Map<String, Object> payload;
+  JsonResponse response;
+
+  @Inject public JsonActionRunner(@JsonPayload Map<String, Object> payload, JsonResponse response) {
+    this.payload = payload;
+    this.response = response;
+  }
 
   /** Delegates request to {@code action}. */
   public void run(JsonAction action) {