* Add elementwise_sub_mkldnn_op without grad

* Add test to static_mode_white_list

* Refactor code, change license years

* Remove invalid grad implementation

* Fix element_wise_sub_op test

* Fix CI Approval error

* Remove unnecessary EltwiseSubMKLDNNGradKernel class

* Fix CI Approval 2

* Fix CI Approval 3

* Fix CI Approval Attempt #4

* Fix CI Approve Attempt #5

* Fix CI Approval Attempt #6

* Fix CI Approval Attemt #7

* Change test names containing add to sub

* Fix old tests testing add instead of sub

* Copy grad implementation from elementwise_add_mkldnn

* CI test fix attempt

* Revert "CI test fix attempt"

This reverts commit c647cacf41e6a87c715385a185de5cbf65fc8900.

* Fix CI attempt 2

* Fix elementwise_sub tests, temporary mkldnn broadcast test disable

* Add working implementation of elementwise_sub grad

* Fix build errors caused by pull

* Fix format error

* Fix format error 2

* Disable elementwise_sub_mkldnn test on GPU

* Apply fix for paddle.fluid import

* Revert changes of test_elementwise_sub and Fix mkldnn test

* Revert "Apply fix for paddle.fluid import"

This reverts commit fc3b122fec8e12f2bcb32928a2685ba4d20fd742.

* fix bug of module 'paddle' has no attribute 'fluid' for python3.6 (#35862)

* Add changes suggested by reviewers

* Change @unittest.skipIf... to @OpTestTool.skip_if_not_cpu_bf16() to satisfy Approval CI

* Remove check_dygraph=False to satisify CI Approval
Co-authored-by: Nzhangbo9674 <82555433+zhangbo9674@users.noreply.github.com>