deleteAccount method
Implementation
Future<void> deleteAccount(String? address) async {
_deleteKeyPair(address);
final mnemonics = Map.of(_storage.encryptedMnemonics.val);
mnemonics.remove(address);
_storage.encryptedMnemonics.val = mnemonics;
final privateKeys = Map.of(_storage.encryptedPrivateKeys.val);
privateKeys.remove(address);
_storage.encryptedPrivateKeys.val = privateKeys;
}