Outdated comment

https://github.com/bevyengine/naga_oil/blame/e315342e0196e85fbe5e5c3c3950254baa730aad/src/compose/mod.rs#L1418

I saw this comment, and thought that perhaps it was meant to be a help in upgrading naga_oil. However the code it links too was entirely unhelpful, and looking at the blame, it comes from earlier when this function actually did take subgroup_stages.