TextEditor: Clean forward declaration

Change-Id: If338617551893e3ce3c7a68ff1abfc60de8cf610
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/texteditor/texteditor.h

@@ -52,11 +52,9 @@ QT_END_NAMESPACE
 namespace TextEditor {
 class TextDocument;
 class BaseHoverHandler;
-class TabSettings;
 class RefactorOverlay;
 struct RefactorMarker;
 class SyntaxHighlighter;
-class IAssistMonitorInterface;
 class AssistInterface;
 class IAssistProvider;
 class ICodeStylePreferences;