Fix most lint warnings

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

desktop/app/src/utils/exportData.tsx

@@ -94,10 +94,6 @@ type ProcessNotificationStatesOptions = {
   statusUpdate?: (msg: string) => void;
 };
 
-type SerializePluginStatesOptions = {
-  pluginStates: PluginStatesState;
-};
-
 type PluginsToProcess = {
   pluginKey: string;
   pluginId: string;

desktop/app/src/utils/iOSContainerUtility.tsx

@@ -15,7 +15,6 @@ import {killOrphanedInstrumentsProcesses} from './processCleanup';
 import {reportPlatformFailures} from './metrics';
 import {promises, constants} from 'fs';
 import memoize from 'lodash.memoize';
-import GK from '../fb-stubs/GK';
 import {notNull} from './typeUtils';
 
 // Use debug to get helpful logs when idb fails

desktop/app/src/utils/serialization.tsx

@@ -27,7 +27,7 @@ export function deserialize(str: string): any {
 }
 
 function processArray(
-  element: any,
+  _element: any,
   array: Array<any>,
   stack: Array<any>,
   dict: Map<any, any>,
@@ -50,7 +50,7 @@ function processArray(
 }
 
 function processKeyValuePair(
-  element: any,
+  _element: any,
   key: any,
   value: any,
   stack: Array<any>,

desktop/app/src/utils/snap.tsx

@@ -112,7 +112,7 @@ export function maybeSnapLeft(
 }
 
 export function maybeSnapTop(
-  props: Rect,
+  _props: Rect,
   windows: Array<Rect>,
   top: number,
 ): number {