Clang*: Use new plugin test setup scheme

Change-Id: I636b93d74b4f9ab9ade28c46c6e84b461ccf34be
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangformat/clangformatplugin.h

@@ -16,7 +16,6 @@ class ClangFormatPlugin : public ExtensionSystem::IPlugin
 
     ~ClangFormatPlugin() override;
     void initialize() final;
-    QVector<QObject *> createTestObjects() const override;
 
     TextEditor::ICodeStylePreferencesFactory *m_factory = nullptr;
 };