Delete outdated *.md files
Twelve docs that no longer track real work or describe the current
fork. Removed:
ocaml-tls/{attacks,sni,design}.md — pre-fork architecture notes from
mirleft/ocaml-tls that reference 2014 CVEs, polarssl, Lwt/Async
flows; nothing in the current Eio-based fork's design.
memtrace/CONTRIBUTING.md — Jane Street upstream guide pointing at
github.com PRs, doesn't apply on tangled.
ocaml-requests/HTTP2_{IMPLEMENTATION_PLAN,CONPOOL_INTEGRATION}.md —
1500 lines combined for an HTTP/2 rollout that hasn't moved in 6+
weeks; revive from git history if/when the work restarts.
merlint/TODO.md, merlint/todo/{new_rules,codes,duplication}.md,
ocaml-sqlite/TODO.md, prune/TODO.md — stale TODO/proposal lists,
last touched 6+ weeks ago. Active TODOs (monopam, irmin, jwt,
cookie, chor, requests SPEC-TODO, claude ARCHITECTURE) all kept.
Also drop the now-empty merlint/todo/ directory and roll in dune fmt
fallout for irmin/test/bench/dune.