[thumbnailer] Don't reimplement flags()

It does the same thing as the default impl

src/thumbnailer/itinerarycreator.cpp

@@ -60,9 +60,4 @@ bool ItineraryCreator::create(const QString &path, int width, int height, QImage
     return false;
 }
 
-ThumbCreator::Flags ItineraryCreator::flags() const
-{
-    return None;
-}
-
 #include "itinerarycreator.moc"

src/thumbnailer/itinerarycreator.h

@@ -19,7 +19,6 @@ public:
     ~ItineraryCreator() override;
 
     bool create(const QString &path, int width, int height, QImage &image) override;
-    Flags flags() const override;
 };
 
 #endif // ITINERARYCREATOR_H