`ipv6-address-zoned` typedef does not follow W3C standard XSD regex pattern

[sengleung]

pattern statements follow the W3C standard XSD regex pattern (as per RFC6020/RFC7950) so regex anchors (^ and $) are implicit and are not required. Regex anchors are covered by the oc-ext:posix-pattern POSIX regex pattern extension statement.

See #44 for background. Similar changes have been done previously like #534.