Merge bitcoin#18424: qt: Use parent-child relation to manage lifetime of OptionsModel object

8e08d00 qt: Use parent-child relation to manage lifetime of OptionsModel object (Hennadii Stepanov)

Pull request description:

  Both `BitcoinApplication` and `OptionsModel` classes are derived from the `QObject` class, therefore a parent-child relation could be established to manage the lifetime of an `OptionsModel` object:
  https://github.com/bitcoin/bitcoin/blob/5236b2e267a58870239673c7ec85e5df0cb8fc8e/src/qt/optionsmodel.cpp#L29-L30

  This PR does not change behavior.

ACKs for top commit:
  jonasschnelli:
    utACK 8e08d00
  promag:
    ACK 8e08d00.

Tree-SHA512: 0223dddf5ba28b0bfaefeda1b03b4ff95bf7e7d0c1e7b32368171e561813e22129f2a664f09279fa3b4fa63259b7680d55aa3fe66db9c7ae0039b7f529777ec3

Author: jonasschnelli

src/qt/bitcoin.cpp

@@ -228,8 +228,6 @@ BitcoinApplication::~BitcoinApplication()
         settings.clear();
         settings.sync();
     }
-    delete optionsModel;
-    optionsModel = nullptr;
 }
 
 #ifdef ENABLE_WALLET
@@ -241,7 +239,7 @@ void BitcoinApplication::createPaymentServer()
 
 void BitcoinApplication::createOptionsModel(bool resetSettings)
 {
-    optionsModel = new OptionsModel(m_node, nullptr, resetSettings);
+    optionsModel = new OptionsModel(m_node, this, resetSettings);
 }
 
 void BitcoinApplication::createWindow(const NetworkStyle *networkStyle)