Declare post type support based on the admin setting and allow overwrite

includes/amp-helper-functions.php

@@ -18,7 +18,7 @@ function amp_get_permalink( $post_id ) {
 }
 
 function post_supports_amp( $post ) {
-	// Because `add_rewrite_endpoint` doesn't let us target specific post_types :(.
+	// Because `add_rewrite_endpoint` doesn't let us target specific post_types.
 	if ( ! post_type_supports( $post->post_type, AMP_QUERY_VAR ) ) {
 		return false;
 	}