Do not require images in about.js and share.js (#6622)

They are already required by common.js.

app/javascript/packs/about.js

 import loadPolyfills from '../mastodon/load_polyfills';
 
-require.context('../images/', true);
-
 function loaded() {
   const TimelineContainer = require('../mastodon/containers/timeline_container').default;
   const React             = require('react');

app/javascript/packs/share.js

 import loadPolyfills from '../mastodon/load_polyfills';
 
-require.context('../images/', true);
-
 function loaded() {
   const ComposeContainer = require('../mastodon/containers/compose_container').default;
   const React = require('react');