fix(brand): the in-app release notes were still Cake's

The What's New screen read "Add support for Bitcoin Lightning / New Design".
That file has never been touched since it was inherited; the last three commits
against it are upstream Cake release candidates. It shipped in 1.0.3.

It now describes what this release actually changed, one line per bullet, which
is the format the screen splits on.

The screen also chose between two files based on isMoneroOnly, and the
monero.com one it named does not exist in this repository. Any build where that
flag went true would have thrown on a missing asset instead of showing notes.
Hash Bags ships eleven chains so the flag is always false, which is the only
reason it never fired. One file now, and the import that existed solely for
that branch is gone.

Also removes assets/images/cupcake.png, which nothing in the repository
references. The cupcake SVG stays: HardwareWalletType.cupcake is a third-party
airgapped signer sitting in a list beside Ledger and Trezor, so it is interop,
not somebody else's branding.

assets/text/Release_Notes.txt

@@ -1,2 +1,5 @@
-Add support for Bitcoin Lightning
-New Design
+Wownero and Monero now fly out of the bag when you send
+Fixed the app icon and logo showing the wrong artwork
+Fixed a crash when using Polygon wallets
+The Wownero logo no longer appears as a grey circle
+Error reports now identify the exact app build

lib/src/screens/release_notes/release_notes_screen.dart

@@ -1,7 +1,6 @@
 import 'dart:convert';
 import 'package:hash_wallet/src/widgets/alert_background.dart';
 import 'package:hash_wallet/src/widgets/alert_close_button.dart';
-import 'package:hash_wallet/wallet_type_utils.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
@@ -13,8 +12,13 @@ class ReleaseNotesScreen extends StatelessWidget {
   final String title;
 
   Future<List<String>> _loadStrings() async {
-    String notesContent = await rootBundle.loadString(
-        isMoneroOnly ? 'assets/text/Monerocom_Release_Notes.txt' : 'assets/text/Release_Notes.txt');
+    // One notes file. The monero.com branch this inherited pointed at
+    // Monerocom_Release_Notes.txt, which does not exist in this repository, so
+    // any build where isMoneroOnly went true would have thrown here rather than
+    // shown release notes. Hash Bags ships many chains and that flag is always
+    // false, which is the only reason it never fired.
+    String notesContent =
+        await rootBundle.loadString('assets/text/Release_Notes.txt');
     return LineSplitter().convert(notesContent);
   }