Fix 7 stale CODEOWNERS paths, remove 6 dead rules - #193745

Summary

Resolves stale references in CODEOWNERS. The lines themselves were left unchanged while the paths they referenced disappeared from the tree.

7 one-line edits resolve the stale references:

• Update CODEOWNERS lines 41-45 to: /torch/ao/quantization/, /torch/nn/intrinsic/, /torch/nn/quantized/, /torch/nn/quantizable/, /torch/nn/qat/
• Update CODEOWNERS line 193 to: /docs/source/notes/get_start_xpu.md
• Update CODEOWNERS line 253 to: /aten/src/ATen/native/ScaledBlas*

Removed 6 dead rules: 4 caffe2/**/hip rules, /torch/utils/pytree/ (already covered by /torch/utils/_pytree.py above), /aten/src/ATen/cuda/CUDAScaledBlas.h (covered by the glob).

Test

# the stale line
sed -n '41p' CODEOWNERS
# tracked files under the referenced path, 0 before this PR
git ls-files -- 'torch/ao/quantization' | wc -l
git ls-files -- 'aten/src/ATen/native/ScaledBlas*' | wc -l
git ls-files -- 'caffe2/core/hip' 'caffe2/utils/hip' | wc -l

Additional information

Since the move, the quantization rules were stale for 1459 days.
I found this mismatch in your repo while analyzing public data with my tool: https://github.com/DanielSwift1992/gate. If you need more details, happy to share.