[LICM][SimplifyCFG] Ignore frees for writable dereferenceability check (#202589)
Both of these places only explicitly check for dereferenceability
because this is required for the `writable` attribute. Actual
dereferenceability has already been established at this point, e.g.
based on a prior access. As such, we can ignore frees here. We only care
that the argument has an appropriately sized `dereferenceable`
attribute.