Remove redundant filters

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](https://github.com/WP-API/WP-API/blob/5dfce405e8c84adf6e9491775eff22fe53725e21/lib/class-wp-json-customposttype.php#L41:L42) in its constructor and `WP_JSON_Pages` extends `WP_JSON_CustomPostType `.