Remove unnecessary dynamic casts left over from old geometry design

Signed-off-by: Taylor Braun-Jones <taylor.braun-jones@ge.com>
Merge branch 'bug-18091-SlicedGeometry3D-remove-unnecessary-dynamic-casts'

* bug-18091-SlicedGeometry3D-remove-unnecessary-dynamic-casts:
  Remove unnecessary dynamic casts left over from old geometry design