Decommission deprecated MD5HashValue and Crc32cChecksumValue types

These storage types were deprecated as part of https://github.com/googleapis/google-cloud-cpp/pull/16311. They should be removed 6 months after deprecation, roughly January 2027. Until that time several test.cc files have been updated to include `google/cloud/internal/disable_deprecation_warnings.inc`. When these types are removed, those deprecation includes should also be removed.

Search the repository for MD5HashValue, Crc32cChecksumValue, and google/cloud/internal/disable_deprecation_warnings.inc to identify their definitions, uses, and affected test.cc files. Confirm the six-month deprecation period has elapsed, remove the deprecated types and associated warning-suppression includes, then run the relevant tests to verify the cleanup.

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