opam: retag 20+ packages with canonical E915 vocabulary

Covers every package whose .opam was missing tags, misspelled a
singleton tag, or only carried a foreign org marker. The canonical
vocabulary now lives in .merlint as E915's topics: list; this pass
makes the monorepo pass E915 on the packages whose dune-project is
the source of truth.

Cleanups: drop singletons cop1/sle/sdls/uslp/s3/sdk; rename log to
logging (json-logs, vlog); add org:blacksun to formerly-Mirage-only
packages (ca-certs, tar, tls, x509, crypto-ec).

Additions to packages missing tags: cfdp-eio, cop1-eio, ltp-eio,
scc-eio, sdls-eio, sle-eio, yamlrw-eio, yamlrw-unix, ocaml-merlin,
scitt-atp, atp-lexicon-scitt, and 10 ocaml-atp subpackages.