Revert #755

Attempt to fix issues with removeChildren and manageChildren bugs,
causing exceptions from RCTUIManager
Related to #258 and #848

https://github.com/facebook/react-native/issues/23350
https://github.com/FormidableLabs/victory-native/issues/432
https://github.com/indiespirit/react-native-chart-kit/issues/62
https://github.com/JesperLekland/react-native-svg-charts/pull/280
https://github.com/JesperLekland/react-native-svg-charts/issues/244

ios/ViewManagers/RNSVGNodeManager.m

@@ -151,6 +151,11 @@ RCT_EXPORT_MODULE()
     return [self node];
 }
 
+- (RCTShadowView *)shadowView
+{
+    return nil;
+}
+
 RCT_EXPORT_VIEW_PROPERTY(name, NSString)
 RCT_EXPORT_VIEW_PROPERTY(opacity, CGFloat)
 RCT_EXPORT_VIEW_PROPERTY(matrix, CGAffineTransform)