I think there is some confusion.
Both the question and the only answer suggest putting a rules section in the tsconfig.json. This is something I’ve never heard of, and it is not mentioned in the docs or in the official schema.
Also, the question is about disabling the rule in eslint so the rule change should go in the .eslintrc.json file (or the eslintConfig section in the package.json as considered in the question).
But this is typescript and typescript-eslint so the rule should be:
> "@typescript-eslint/no-unused-vars" : "off"
And the hacky solution proposed in an answer that someone linked to needs to be changed to (note that answer is about eslint for js, not ts).
/* eslint-disable @typescript-eslint/no-unused-vars */
And those solutions work for me using…
+-- eslint@6.5.1
+-- @typescript-eslint/eslint-plugin@2.3.2
+-- @typescript-eslint/parser@2.3.2