Summary:
I noticed that after the typescript upgrade, I got several weird positives from ESLint (like unused parameters in a type definition, which are obviously always unused, e.g. `type onClick = (e: Event) => void`). After some investigation, it turned out these warnings are generated by eslint, but that those rules should be performaned by typescript/eslint instead. For future reference to which rules this applies:
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/README.md#extension-rules
Updated the config, and while at it, fixed all warnings in our codebase, except for `react-hooks/exhaustive-deps` warnings, since those require semantic changes.
This reduces the amount of eslint warnings from 86 to 39.
Reviewed By: passy
Differential Revision: D23905630
fbshipit-source-id: 0557708fd9ec6b17840a3c191e7d3baf225bdf23
ecf4cff7cf