Even if skinning is not fully implemented on FL0, we have clients which depend
on materials with skinning variants that otherwise could easily be converted to
FL0 materials. There are two proper ways to deal with this:
1. Support skinning/morphing in Feature Level 0.
2. Allow ESSL 1.0 code and ESSL 3.0 code to support different sets of variants.
However, the simplest solution is to just include skinning/morphing variants,
but disable codegen for ESSL 1.0 code, making them identical to the base
variants. This shouldn't increase the file size much due to the dictionary
deflation. Of course, skinning will not work correctly on FL0, but this has
always been the case. Future work here would be to properly implement one of the
two solutions described above.