Move git specific stuff out of diff editor plugin

Move it to the git plugin.

Change-Id: I8151573ed50df70776f7ebf0475dd41fb84fae83
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/diffeditor/diffeditordocument.h

@@ -90,7 +90,6 @@ signals:
     void temporaryStateChanged();
     void documentChanged();
     void descriptionChanged();
-    void requestMoreInformation();
 
 private:
     void beginReload();