DiffEditor: Make SideBySideDiffEditorWidget internal

Change-Id: I794282d23dc13525fbc9ad327cfa8dce2c28fbca
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/diffeditor/sidebysidediffeditorwidget.cpp

@@ -71,8 +71,7 @@ using namespace TextEditor;
 using namespace Utils;
 
 namespace DiffEditor {
-
-using namespace Internal;
+namespace Internal {
 
 ////////////////////////
 /*
@@ -1582,6 +1581,7 @@ void SideBySideDiffEditorWidget::synchronizeFoldings(SideDiffEditorWidget *sourc
 }
 #endif
 
+} // namespace Internal
 } // namespace DiffEditor
 
 #include "sidebysidediffeditorwidget.moc"