[Tutorials] Update matrix multiply for beta 2.

[awkeep-aws]

Updated the matrix_multiply_nki_kernel.py for the NKI beta 2.

Note: nki.benchmark is not yet implemented, removed code that called it.

Issue #, if available:

N/A

Description of changes:

Update the matrix multiply example from beta 1 to beta 2 NKI syntax.

Testing:

Please see detailed unit test requirements in the CONTRIBUTING.md

• The change is covered by numeric check using nki.baremetal Note: Not available in NKI beta 2 (yet)
• The change is covered by performance benchmark test using nki.benchmark Note: Not available in NKI beta 2 (yet)
• The change is covered by end-to-end integration test

Pull Request Checklist

• I have filled in all the required field in the template
• I have tested locally that all the tests pass
• By submitting this pull request, I confirm that my contribution is made under the terms of the MIT-0 license.