Revert "Use MLIR op lowering of FusedBatchNormV3 and FusedBatchNormGradV3 for tf2xla"
Reverts commit https://github.com/tensorflow/tensorflow/commit/676af55749f95c486c6fce5b8b550c5412e28a5b

We found via git bisect that this commit breaks convergence (loss goes to NaN) for a TF Keras Resnet50 model with XLA enabled.