Blender Git Loki

USD: Library upgrade 19.11 ?�20.02

This upgrade required a few changes:
- Some parts of our patch are no longer necessary, as the USD library
now includes those changes.
- The rest of the patch needed adjustment as the `pxr/base/lib/*`
directories in USD's source code have moved to `pxr/base/*`.
- Updated library names on Windows -- thanks @LazyDodo.

Note that this does not enable the USD Python API for inclusion in
Blender. It just aims at being an as-simple-as-possible version upgrade
of the USD library.