[oneDNN] Remove oneDNN eltment-wise ops in mkl_relu_op.cc
@penpornk Hi Penporn, all the listed element-wise ops are registered with MKL layout op label. Now oneDNN ops only support native format, thus Mkl tensors are not used any more in graph rewriting.  

As part of code cleanup effort (hopefully reduce compilation time, and a little execution time w/o if/else), we remove thie implementation of mkl_relu_op.cc and related tests. In near future, I will submit a sequence of PRs to clean up all "Mkl layout" related implementation for all oneDNN ops, as well as lots of outdated "layout" comments in core/common_runtime/mkl_layout_pass.cc. 

Thanks Hi @penpornk Can you please review this PR ? Thank you! @penpornk  Hi Penporn, please help to review this PR. A follow-up PR will clean up all MKL layout propagation code (for instance, get rid of MKL tensor stuff) in core/common_runtime/mkl_layout_pass.cc (remove 1000+ lines of source code which is not functioning any more).  THANKS!   -GZ Hi @penpornk Can you please review this PR ? Thank you!

 Hi @penpornk Can you please review this PR ? Thank you!
Remove the following oneDNN ops which are not supported since TF2.15 (all registered ops used to support MKL layout format):

Relu, ReluGrad, Relu6, Relu6Grad, Elu, EluGrad, Tanh, TanhGrad, LeakyRelu, LeakyReluGrad

Related C++ test cases are also removed