Delete some KES functionality

[ramondeklein]

Some KES functionality should be removed from the MinIO console, because of PR See minio/minio#19368. The following functionality isn't available anymore:

• Importing keys
• Deleting keys

If there's any functionality that list identities or policies, then it should be removed as well. These APIs are also not available anymore. Note that KES was never able to modify identities or policies, so these APIs have never worked.

The ListKeys method returns []KMSKeyInfo, but only the name is set. All other information is always empty (see also minio/madmin-go#289). We should either add this information or remove the columns in the console.

It involves the following fields:

See minio/minio#20125 and minio/madmin-go#289 for more context.

[ramondeklein]

CreatedBy and CreatedAt will be added to MinIO, so we don't need to remove these columns. See minio/minio#20132.