[MLIR][Python] remove PyYAML as a dep (#169145)
PyYAML is not an actual use-time/runtime dependency of our bindings. It
is necessary only if someone wants to regenerate
`LinalgNamedStructuredOps.yaml`:
https://github.com/llvm/llvm-project/blob/93097b2d47c87bf5eee0a2612d961c7a01831eab/mlir/tools/mlir-linalg-ods-gen/update_core_linalg_named_ops.sh.in#L29
This PR does the minimal refactor to remove the need during actual run/use time.
