Remove MIOpen softmax & batchnorm

[pxl-th]

NNlib has pure Julia implementation for both and MIOpen softmax has issues: ROCm/MIOpen#2966

[atamazov]

Note that ROCm/MIOpen#2966 won't manifest itself unless the same instance of the library is used to get softmax for different datatypes.

The fix in on the way: ROCm/MIOpen#2992

[pxl-th]

Note that ROCm/MIOpen#2966 won't manifest itself unless the same instance of the library is used to get softmax for different datatypes.

Yes, that's exactly what we were doing. We run tests for different types in the same session and users are generally not restricted to what types they can use.