This was incorrect and had to be reverted. The attributes are still necessary for current behavior.

Certain IPC requests to the attribute manager, CIB manager, and controller have an acl_target XML attribute with the ACL user name. Before 1.1.12, this was attr_user for the attribute manager, cib_user for the CIB manager, and crm_user or lrmd_ipc_user for the controller. pcmk__update_acl_user() sets both the current and legacy attributes for compatibility in rolling upgrades. Once we drop support for rolling upgrades and remote client connections from earlier versions (see the subtasks), we can stop adding the legacy attributes.

Basically all that needs to be done is drop the field argument to pcmk__update_acl_user().

Also before 1.1.12, the CIB had different syntax for ACLs. These were changed at the time in the schema via transforms, but the CIB manager doesn't upgrade CIB schemas, so it had to support the old syntax during rolling upgrades. This support and related cts-cli tests have already been dropped for 3.0.0 via CLPR#3508.