[nir] GN build: remove magma_python_path

It's not necessary because mako is specified as a library,
and we want to get rid of magma_python_path.

Change-Id: Id576c5ab336aca9328345790b1e56ae07022ca89
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1012107
Reviewed-by: John Bauman <jbauman@google.com>
Commit-Queue: Craig Stout <cstout@google.com>
2 files changed