Fix linter errors

```
/home/runner/work/react-map-gl/react-map-gl/examples/get-started/hook/controls.jsx
Error:   53:35  error  Expected to return a value at the end of arrow function  consistent-return

/home/runner/work/react-map-gl/react-map-gl/examples/get-started/hook/controls2.js
Error:   1:9  error  'useMap' is defined but never used  no-unused-vars

/home/runner/work/react-map-gl/react-map-gl/examples/get-started/hook/map.jsx
Error:   2:14  error  'useMap' is defined but never used  no-unused-vars
```

examples/get-started/hook/controls.jsx

@@ -51,7 +51,7 @@ export default function Controls() {
   }, []);
 
   const onSubmit = useCallback(() => {
-    if (!mymap) return undefined;
+    if (!mymap) return;
 
     const [lng, lat] = inputValue.split(',').map(Number);
     if (Math.abs(lng) <= 180 && Math.abs(lat) <= 85) {

examples/get-started/hook/controls2.js

@@ -1,4 +1,4 @@
-import {useMap} from 'react-map-gl';
+// import {useMap} from 'react-map-gl';
 
 export default function Controls2() {
   /**

examples/get-started/hook/map.jsx

@@ -1,5 +1,6 @@
 import * as React from 'react';
-import Map, {useMap} from 'react-map-gl';
+import Map from 'react-map-gl';
+// import {useMap} from 'react-map-gl';
 
 import 'mapbox-gl/dist/mapbox-gl.css';
 import Controls2 from './controls2';