PyTorch: [BE][MPS] Remove test_mps.py tests already covered by OpInfo (#200579)

Executive Summary

Removes 34 hand-written CPU-vs-MPS comparison tests (29 in TestMPS , 5 in MatmulTest , plus the now-unused MatmulTest._helper ) whose calls are all already exercised by TestConsistency OpInfo samples. Coverage was checked by recording, under a dispatch mode, every aten call each test makes on MPS (overload, input dtypes, 0-d/empty/non-contiguous inputs, which arguments are passed, out= /in-place variant) and comparing against the calls made by OpInfo samples for every dtype TestConsistency does not xfail on MPS.

Hyperscale Open Source & Cloud Infrastructure Review

From an infrastructure engineering, cloud-native scale, and hyperscale governance standpoint: - **Hyperscale Provenance:** Open-sourcing internal frameworks subjects proprietary systems to rigorous public analysis. - **De-facto Standard Cohesion:** Publishing enterprise tooling establishes interoperable specifications across distributed execution. - **Vendor Decoupling:** Platform engineers can inspect underlying telemetry and memory layouts without black-box vendor lock-in.

Impact on the Open Ecosystem

Bridges enterprise engineering scale with independent, reproducible open-source software stacks.