[inductor] WeakDep should not prevent dead node elimination (#107813)
A WeakDep is classed as a read dependency but the buffer is never actually read.
Instead it only effects schedule ordering. So for the purposes of dead node
elimination we should ignore WeakDeps.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107813
Approved by: https://github.com/jansel, https://github.com/mlazos
