chore(train): remove unused MTP helper #5660

Job	Run time
pre-flight / pre-flight	12s
UV - Python - ARM64/Darwin - No CUDA	56s
UV - Python - AMD64/Linux - No CUDA	1m 38s
Build CUDA wheelhouse - Python3.12 - AMD64/Linux - NGC CUDA	3m 0s
UV - Python3.12 - AMD64/Linux - NGC CUDA	2m 45s
Pip - Python3.10 - ARM64/Darwin - No CUDA	2m 37s
Pip - Python3.12 - ARM64/Darwin - No CUDA	1m 53s
Pip - Python3.11 - AMD64/Linux - No CUDA	2m 15s
Pip - Python3.12 - AMD64/Linux - No CUDA	2m 7s
Pip - Python3.11 - ARM64/Darwin - No CUDA	1m 39s
Pip - Python3.10 - AMD64/Linux - No CUDA	2m 7s
Install test summary	1s
Pip - Python${{ matrix.python-version }}${{ (((matrix.extra-groups != '') && format('[{0}]', matrix.extra-groups)) \|\| '') }} - AMD64/Linux - NGC CUDA	1s
	21m 11s

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