Remove wheel-size validators (moved to pytorch-gha-infra) (#8323)

## Summary

The nightly **wheel-size regression detector** and its
**`wheel-size-analyzer` skill** have moved to
**meta-pytorch/pytorch-gha-infra**, where a daily workflow runs the
skill across all wheel platforms (Linux/manywheel, Windows x86, macOS
arm64) and files a `dev-infra-ai-alert` issue on a significant size
increase (the same alert surface Treehugger uses).

This PR removes them from test-infra, along with the older binary-size
validator workflows and their tooling.

### Deleted — moved to gha-infra
- `.github/workflows/nightly-wheel-size-regression.yml` (added in #8317)
- `.claude/skills/wheel-size-analyzer/` (added in #7827)

### Deleted — old wheel-size validators
- `.github/workflows/validate-pypi-wheel-binary-size.yml`
- `.github/workflows/test-binary-size-validation.yml`
- `.github/workflows/validate-repackaged-binary-sizes.yml`
- `tools/binary_size_validation/` — only consumed by the two removed
workflows

### Also
- Drop the `validate-repackaged-binary-sizes.yml` entry from
`.lintrunner.toml`.

### Safety
Verified none of these are invoked by `validate-binaries.yml` or any
nightly-binary validation workflow
(`validate-{linux,windows,aarch64-linux,macos-arm64}-binaries.yml`);
none are `workflow_call` reusables. The only remaining mention of the
PyPI validator's job name is a generic regex-filter unit-test fixture in
`tools/torchci/tests/test_check_alerts.py`, left untouched.

Author: atalman