Remove unused variables

Mark some of them with Q_UNUSED, since it looks like
sometimes the copy is done on purpose, to force detach
or used for some hack with memory management.
In one case make unused variable used again.

Change-Id: I3825cd3399fa63bf6e12173c64509287d4a125e5
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/android/avddialog.cpp

@@ -146,7 +146,6 @@ void AvdDialog::parseDeviceDefinitionsList()
         if (line.startsWith("---------") || line.isEmpty()) {
             DeviceDefinitionStruct deviceDefinition;
             for (const QString &line : avdDeviceInfo) {
-                QString value;
                 if (line.contains("id:")) {
                     deviceDefinition.name_id = line.split("or").at(1);
                     deviceDefinition.name_id = deviceDefinition.name_id.remove(0, 1).remove('"');