CppTools: Use a normal plugin pimpl member for CppModelManager

Change-Id: Id2c4b098084808070ef91de13c8338184e52141d
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/cpptools/cpptoolsplugin.cpp

@@ -82,7 +82,6 @@ class CppToolsPluginPrivate
 public:
     CppToolsPluginPrivate()
     {
-        CppModelManager::createCppModelManager(m_instance);
         m_settings = new CppToolsSettings(m_instance); // force registration of cpp tools settings
         m_codeModelSettings.fromSettings(ICore::settings());
         m_cppCodeStyleSettingsPage = new CppCodeStyleSettingsPage;
@@ -96,6 +95,7 @@ public:
     }
 
     StringTable stringTable;
+    CppModelManager modelManager;
     CppCodeModelSettings m_codeModelSettings;
     CppToolsSettings *m_settings = nullptr;
     CppFileSettings m_fileSettings;