mul: remove opmath cast sequence (#9663) #13834

Job	Run time
Check Code Changes / check_files	17s
Build PyTorch/XLA / build	23m 20s
report-no-code-changes	-1s
TPU tests / tpu-test (test/tpu/run_pallas_test.sh)	11m 30s
TPU tests / tpu-test (test/tpu/run_tests.sh)	32m 35s
CPU tests / test (python_tests, xla_op2)	9m 27s
TPU tests / tpu-test (test/tpu/run_expensive_test_1.sh)	31m 30s
CPU tests / test (python_tests, xla_op3)	13m 57s
CPU tests / test (python_tests, xla_op4)	6m 50s
CPU tests / test (python_tests, xla_op1)	18m 17s
CPU tests / test (benchmark_tests)	12m 28s
TPU tests / tpu-test (test/tpu/run_expensive_test_2.sh)	32m 37s
CPU tests / test (python_tests, xla_op5)	8m 33s
TPU tests / tpu-test (test/tpu/run_training_tests.sh)	18m 52s
CPU tests / test (cpp_tests)	14m 21s
CPU tests / test (python_tests, torch_mp_op)	9m 59s
Build docs / build-docs	1m 56s
torchprime tests	0s
	4h 6m 28s

Provide feedback