libhext/HtmlTag: remove visibility attribute on enum definition
libhext/HtmlTag: remove visibility attribute on enum definition

Enum type definitions aren't symbols, so there's no reason to specify
symbol visibility.

thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext