[XLA:GPU] Use raw HloInstruction pointers instead of HloInstructionAdaptor in caches.
[XLA:GPU] Use raw HloInstruction pointers instead of HloInstructionAdaptor in caches.

HloInstructionAdaptor should be an "iterator" to HloFusionAdaptor. Creating an instruction adaptor without fusion adaptor doesn't make sense.

Using raw pointer inside one pass is fine, because instruction are only deleted after the pass. If this becomes a problem at some point, we should used a separate abstraction to compare unique_ids.
