Alternate fix for bug [#34369], where invalid polygon normals could be saved in the mesh data and in the file.

This was from initial BMesh merge, but should not have been added in since face normals are calculated and stored in the DerivedMesh.

Toggling editmode would remove poly-normals so its unlikely anything relies on this custom-data.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55074 954f8c5b-7b00-dc11-b283-0030488c597c