McuSupport: Fix compiler warnings

- override missing for mock methods
- remove unused variable

Change-Id: If703b60dece417fc7dc004d67966f2b6b8281990
Reviewed-by: Piotr Mućko <piotr.mucko@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/mcusupport/test/unittest.cpp

@@ -106,7 +106,6 @@ const char unsupported[]{"unsupported"};
 const char vendor[]{"target_vendor"};
 const QString settingsPrefix = QLatin1String(Constants::SETTINGS_GROUP) + '/'
                                + QLatin1String(Constants::SETTINGS_KEY_PACKAGE_PREFIX);
-const char qmlToCppSuffixPath[]{"bin/qmltocpp"};
 
 const QString unsupportedToolchainFilePath = QString{qtForMcuSdkPath}
                                              + "/lib/cmake/Qul/toolchain/unsupported.cmake";