Review DeprecatedHookImplementation for removal

[mglaman]

Background

src/Rules/Deprecations/DeprecatedHookImplementation.php was added in November 2023 but has never been registered in rules.neon or extension.neon. It silently does nothing for users of this package.

Problems

1. Never registered — the rule is not wired into any neon config, so no one is getting its checks.
2. Hardcoded and stale — the only specific deprecation it detects is hook_field_widget_multivalue_form_alter (a Drupal 9→10 deprecation), hardcoded with a @todo acknowledging the approach is not extensible or intelligent.
3. Superseded — Drupal 10+ hook deprecations are better handled via the Hook attribute system, which is already covered by other rules in this project.

Proposed resolution

Either:

• Remove src/Rules/Deprecations/DeprecatedHookImplementation.php and its test tests/src/Rules/DeprecatedHookImplementationTest.php — the rule has never been active and the hardcoded hook it targets is an obsolete D9→D10 migration concern.
• Or register and rewrite it using a data-driven approach if detecting deprecated procedural hook implementations is still a desired feature.

Given the narrow scope and the stale hardcoded logic, removal is the cleaner path unless there is a concrete plan to generalize it.