chore: drop upstream gsd issue and pr governance

MSD does not use an issue tracker, and the inherited GSD community gates
auto-closed PR #1 for lacking an issue-numbered title. Remove them:

- workflows: require-issue-link, pr-title-validator,
  auto-close-unsolicited-prs, pr-template-format, close-draft-prs(-sweep),
  auto-label-issues, auto-branch, duplicate-check, duplicate-sweep,
  remove-duplicate-label
- GSD PR and issue templates, plus the scripts only they used
  (require-issue-link-policy, pr-template-policy, pr-changed-files) and
  their tests
- workflow lists in ci-test-scope, ci-pr-mergeability,
  workflow-maintainer-skip, lint-pr-check-project-dir, the docs-guard
  baseline and the conformance tiers
- CONTRIBUTING: PR-against-next flow with no issue or template; PR titles
  are conventional without an issue ref; ADR/PRD files use the PR number
- CONTEXT.md: drop the PR-template predicates (k328, templates-mandatory)

scripts/lib/macos-conformance-tier.generated.cjs

@@ -163,7 +163,6 @@ module.exports = {
   "tests/quick-research.test.cjs",
   "tests/reapply-verify-hunks.test.cjs",
   "tests/refactor-1390-t3-characterization.test.cjs",
-  "tests/require-issue-link-policy.test.cjs",
   "tests/response-language-coverage.test.cjs",
   "tests/retired-artifact-cleanup.test.cjs",
   "tests/review-build-prompt-optional-sections.test.cjs",