Blender Git Loki

Fix T61600: Physics properties inactive when appending objects

This problem existed in 2.79 as well. The rigid body setting is related
to the scene the object was created.

We now clear all the rigid body properties of the appended objects to
prevent them from lingering in this state where they have settings yet
cannot be used in the simulation.

Reviewers: mont29, brecht

Differential Revision: https://developer.blender.org/D4380