Retire the markdownlint and vale docs jobs after an overlap with recheck #3206

Problem

The documentation tests workflow runs markdownlint, vale, and the new recheck job (#3187) side by side.
recheck ports the markdownlint parity settings and the prose rules, so the first two jobs repeat its checks.

Proposal

Keep all three for a few weeks of overlap.
Then compare the findings, port any Vale rule that recheck does not cover yet, and remove the markdownlint and vale jobs and their configuration files in one pull request.

linkcheck stays: it fetches external URLs, which recheck does not do.

Reference

• chore: lint the docs and cookbook Markdown with redocly recheck #3187 and the review thread that proposed the removal.