[XLA] Stop duplicating broadcasts before host memory offloading.
[XLA] Stop duplicating broadcasts before host memory offloading.

`HostOffloader` will do this as needed. As a result, `HostOffloadLegalize` no longer needs to differentiate between pre/post LayoutAssignment.

This requires a change to `TpuCopyNormalizer` to change copies of `"AllocateBuffer"` to clones of `"AllocateBuffer"`. That is because `"AllocateBuffer"` will create a host tensor and host-to-host copies are not supported.

Reverts changelist 641225077

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/13523 from ROCm:ci_hotfit_20240607 931ddf1d5b87c85c3fe1d825665015882d50ef42
