Removed _gemm_batch_old_nm_impl, got rid of using _new_, _old_ in names

[oleksandr-pavlyk]

This PR replaced uses of _old_nm_ functions with _new_nm_ functions, and then removed GemmBatchFunctorThreadNM and the _old_nm_ unused functions.

After this all _new_ and _old_ parts in the functions names were deleted.

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[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞

[coveralls]

coverage: 91.138%. remained the same
when pulling f62ba25 on futher-gemm-code-cleanup
into 275138b on master.

[github-actions]

Array API standard conformance tests for dpctl=0.16.0dev0=py310h15de555_6 ran successfully.
Passed: 906
Failed: 3
Skipped: 86

[ndgrigorian]

I've tested this compared to master, I don't see a significant performance change.

LGTM!