Drop rollout-added Documentation.yml (#51)

## Summary

Drops `.github/workflows/Documentation.yml` that was added by the v2
rollout (merged earlier today). This repo uses a custom
`.github/workflows/Deploy.yml` for docs build + deploy; the standard
`Documentation.yml` from the template would create a duplicate /
conflicting docs path.

The original 2026-05-01 rollout (`#54` for `ITensorDocs.jl`, `#49` for
`ITensorDocsNext.jl`) handled this same exception manually before
merging. This time the file slipped in, so this is the cleanup PR.

Author: mtfishman