Issue #3612485: Remove all code deprecated for removal in 4.0.0

Frank Mablyrequested to merge
issue/domain-3612485:3612485-remove-all-code into 4.x

Removes the module's own @deprecated API, the #[LegacyHook] procedural wrappers (redundant on ^11.4), the emptied .module files, and version-specific compatibility cruft. Internal callers and the test suite are migrated to the replacement APIs; tests use $this->container->get(). See the issue summary for the full per-submodule list.

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