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/scripts/start-dev-server.ts

@@ -142,7 +142,7 @@ function startAssetServer(
 ): Promise<{app: Express; server: http.Server}> {
   const app = express();
 
-  app.use((req, res, next) => {
+  app.use((req, _res, next) => {
     if (knownErrors[req.url] != null) {
       delete knownErrors[req.url];
       outputScreen();
@@ -150,14 +150,14 @@ function startAssetServer(
     next();
   });
 
-  app.use((req, res, next) => {
+  app.use((_req, res, next) => {
     res.header('Cache-Control', 'private, no-cache, no-store, must-revalidate');
     res.header('Expires', '-1');
     res.header('Pragma', 'no-cache');
     next();
   });
 
-  app.post('/_restartElectron', (req, res) => {
+  app.post('/_restartElectron', (_req, res) => {
     if (shutdownElectron) {
       shutdownElectron();
     }
@@ -165,8 +165,8 @@ function startAssetServer(
     res.end();
   });
 
-  app.get('/', (req, res) => {
-    fs.readFile(path.join(staticDir, 'index.dev.html'), (err, content) => {
+  app.get('/', (_req, res) => {
+    fs.readFile(path.join(staticDir, 'index.dev.html'), (_err, content) => {
       res.end(content);
     });
   });