EditorManager: Use interface directly instead of going through ICore

In the majority of cases we were doing that anyways, having two
ways is just needlessly confusing.

Change-Id: Ied362a702c23beee528368d74df1f2aabe5807f8
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/texteditor/basehoverhandler.cpp

@@ -43,7 +43,7 @@ using namespace Core;
 BaseHoverHandler::BaseHoverHandler(QObject *parent) : QObject(parent), m_diagnosticTooltip(false)
 {
     // Listen for editor opened events in order to connect to tooltip/helpid requests
-    connect(ICore::editorManager(), SIGNAL(editorOpened(Core::IEditor*)),
+    connect(Core::EditorManager::instance(), SIGNAL(editorOpened(Core::IEditor*)),
             this, SLOT(editorOpened(Core::IEditor*)));
 }