Remove experimental_adaptive_avx_optimization flag from XNNPACK delegate options
Remove experimental_adaptive_avx_optimization flag from XNNPACK delegate options

It's always on now.

Reverts changelist 637594837

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/13089 from ROCm:ci_reduce_large_row_to_scalar ae97058c01ca57107a2566a6f190d51f5ad4ca0e
