qml: remove '1 month' expiry option.

The list of supported values is in electrum/invoices.py
If the config is set to an unsuported value, the qt app will crash.

electrum/gui/qml/components/controls/RequestExpiryComboBox.qml

@@ -17,7 +17,6 @@ ElComboBox {
             expiresmodel.append({'text': qsTr('1 hour'), 'value': 60*60})
             expiresmodel.append({'text': qsTr('1 day'), 'value': 24*60*60})
             expiresmodel.append({'text': qsTr('1 week'), 'value': 7*24*60*60})
-            expiresmodel.append({'text': qsTr('1 month'), 'value': 31*24*60*60})
             expires.currentIndex = 0
             for (let i=0; i < expiresmodel.count; i++) {
                 if (expiresmodel.get(i).value == Config.requestExpiry) {