unicode: pass a UNICODE_AGE() tripple to utf8_load

Don't bother with pointless string parsing when the caller can just pass
the version in the format that the core expects.  Also remove the
fallback to the latest version that none of the callers actually uses.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>