Remove an additional authorized signer

A member with signers_manage in enforced mode or permissions_manage in legacy mode removes one of the business's additional authorized signers, saying why. No Stable Sea approval is needed: the removal takes effect at once, is recorded on the audit ledger with the member and the reason, and is emailed to Stable Sea compliance, to the business's admins and to the removed person. The signer stays on record as removed, and the same person can be added again later with a new request. The authorized signer on the KYB form (the business's controller at its custodian) cannot be removed here and is unchanged; nothing is sent to the custodian. Answers with the removed signer as they were listed. Refused when the signer is not one of the business's (additional_signer_not_found), was already removed (additional_signer_already_removed, and nothing is recorded), or the reason is blank (signer_change_invalid).