Fix crash on exit

Fixes a crash on exit in ~AnalyzerManager, where
EditorManager::instance() might be already 0.

Change-Id: Ie1d5aa5590d2dd763f5cb8c7e0a8a5e593fd2af6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/editmode.cpp

@@ -93,8 +93,6 @@ EditMode::EditMode() :
 
 EditMode::~EditMode()
 {
-    // Make sure the editor manager does not get deleted
-    EditorManager::instance()->setParent(0);
     delete m_splitter;
 }