SDLPP: add option to remove collisions

sdlpp/sdlpp_renderobject.cpp

@@ -63,6 +63,9 @@ RenderObject::colidesWith( const RenderObject &other ) const {
     }
     return ret;
 }
+void RenderObject::removeCollisions() {
+    collisions.clear();
+}
 bool RenderObject::hasCollisions() const {
     return !collisions.empty();
 }