Backlog#1845 step 8 prerequisite. policy::error::Error carried six variants with zero construction and zero match sites anywhere in the workspace: ErrCredMalformed, CredNotInitialized, NoAccessKey, InvalidToken, InvalidAccessKey, InvalidExpiration. Their only reference was the grouped fallthrough arm in iam's From<policy::error::Error>, whose own dead same-name twins were already removed in backlog#1831 (#6030).
Delete the variants and their display-message test rows; the iam mapping's grouped arm shrinks from eight variants to the two that are actually produced (InvalidServiceType from service_type parsing, JWTError via #[from]). This clears the way for folding the remaining 25-arm hand-written mapping (backlog#1845 step 8).
Ref rustfs/backlog#1845
Zhengchao An
b610d5a55d