Remove redundant filters

[thenbrent]

The JSON REST API plugin hooks WP_JSON_Pages::registerRoutes() to the 'json_endpoints' filter and WP_JSON_Pages::type_archive_link() to the 'json_post_type_data' filter.

This is unnecessary as WP_JSON_CustomPostType already hooks these functions to those filters in its constructor and WP_JSON_Pages extends WP_JSON_CustomPostType.

[rmccue]

I'd actually really like to move those out of the class constructor, since it forces the classes to contain global state. That said, it's a bit annoying to have to do this in plugins all the time, so maybe we need a helper method to register it. Both require docs changes.

[rmccue]

Bumping to 0.9 to do this properly.

[rachelbaker]

Assigning to @rmccue