change defaults for Dropout and BatchNorm #4266

Job	Run time
Build tunix package / Build Tunix wheel	9s
tunix_cpu_unit_tests / run	1m 17s
tunix_tpu_unit_tests / run_prod	12m 5s
tunix_tpu_unit_tests / run_dev	22m 53s
Notify failed build	2s
	36m 26s

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