intl docs: Remove instruction to import bindings file

Previously with `package:flutter_gen`, a manual import of the
bindings file was required because editor/IDE plugins didn't
automatically suggest imports for the `ZulipLocalizations` class.
See:
  https://github.com/dart-lang/linter/issues/3308
  Dart-Code/Dart-Code#3948
  flutter/flutter-intellij#4869

Now that the generated files are located in `lib/generated/l10n`,
IDE plugins provide auto-import suggestions, making the manual
import instruction unnecessary.

Author: rajveermalviya

docs/translation.md

@@ -54,12 +54,7 @@ changes to the ARB file.
 
 ### Using a translated string in the code
 
-To use in our widgets, you need to import the generated bindings:
-```
-import '../generated/l10n/zulip_localizations.dart';
-```
-
-Then in your widget code, pull the localizations object
+To use in your widget code, pull the localizations object
 off of the Flutter build context:
 ```
 Widget build(BuildContext context) {