Remove system methods

[eduard93]

What to do?

https://gist.github.com/bspead/bf23a28029e8d389ac39a3a4af3342bd
https://community.intersystems.com/post/writing-forward-compatible-json-20161

IMPORTANT DISCLAIMER: These macros are being provided as examples and are in no way supported by InterSystems (and they will not be part of the product). Also, after all instances of an application are upgraded to 2016.2 or higher the macros should be removed – they are not intended for permanent inclusion in an application’s code base.

[eduard93]

@kusedr