Cleaning up Veggie Seasons (#2416)

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

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[Discord]:
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veggieseasons/lib/data/app_state.dart

@@ -3,8 +3,8 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
-import 'package:veggieseasons/data/local_veggie_provider.dart';
-import 'package:veggieseasons/data/veggie.dart';
+import 'local_veggie_provider.dart';
+import 'veggie.dart';
 
 class AppState extends ChangeNotifier {
   final List<Veggie> _veggies;

veggieseasons/lib/data/local_veggie_provider.dart

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
-import 'package:veggieseasons/data/veggie.dart';
+import 'veggie.dart';
 
 class LocalVeggieProvider {
   static List<Veggie> veggies = [

veggieseasons/lib/data/preferences.dart

@@ -6,7 +6,7 @@ import 'dart:async';
 
 import 'package:flutter/cupertino.dart';
 import 'package:shared_preferences/shared_preferences.dart';
-import 'package:veggieseasons/data/veggie.dart';
+import 'veggie.dart';
 
 /// A model class that mirrors the options in [SettingsScreen] and stores data
 /// in shared preferences.