Remove React, PureComponent global import, added those imports to files directly

• Remove:
- React, PureComponent global import and added those imports to files directly

app/javascript/gabsocial/features/generic_not_found.js

@@ -1,6 +1,7 @@
+import React from 'react'
 import ColumnIndicator from '../components/column_indicator'
 
-export default class GenericNotFound extends PureComponent {
+export default class GenericNotFound extends React.PureComponent {
 
   render() {
     return (