Move dev-only flags to only exist on composites (#6709)

_isOwnerNecessary was unused.

src/renderers/shared/reconciler/ReactCompositeComponent.js

@@ -169,6 +169,10 @@ var ReactCompositeComponentMixin = {
 
     // ComponentWillUnmount shall only be called once
     this._calledComponentWillUnmount = false;
+
+    if (__DEV__) {
+      this._warnedAboutRefsInRender = false;
+    }
   },
 
   /**

src/renderers/shared/reconciler/instantiateReactComponent.js

@@ -135,11 +135,6 @@ function instantiateReactComponent(node) {
   instance._mountIndex = 0;
   instance._mountImage = null;
 
-  if (__DEV__) {
-    instance._isOwnerNecessary = false;
-    instance._warnedAboutRefsInRender = false;
-  }
-
   if (__DEV__) {
     var debugID = isEmpty ? 0 : nextDebugID++;
     instance._debugID = debugID;