Release: Reduce Requirements

[mikedh]

• sympy is only used implicitly, so move it to a new recommends extra
• recursively delete any test directories included in the docker images
• explicitly assign the uid=499 to the docker user user.
  • system users are uid 100-499, and automatic ones start at 100 and increment
  • this allows upstream docker to do a COPY --link --chown=499 using buildkit without hitting COPY --link not compatible with chown moby/buildkit#2987
• release Preserve texture on slice_plane #2006
  • trimesh.intersections.slice_faces_plane always returns 3 arguments now instead of 2. slice_mesh_plane which is the entry point for most users is unchanged.
• remove trimesh.integrate which was deprecated and not included in any __init__