Photon: Remove duplicate jetpack_photon_url filter (#14323)

There are two calls to add_filter('jetpack_photon_url', 'jetpack_photon_url'): one
is in load_jetpack.php, and one is in functions.photon.php. Clean up this
duplication by removing the add_filter() call in load_jetpack.php.

I chose to put the add_filter() call in functions.photon.php because it looks like
this will be easier to sync with wpcom.

functions.photon.php

@@ -220,6 +220,12 @@ function jetpack_photon_url( $image_url, $args = array(), $scheme = null ) {
 
 	return jetpack_photon_url_scheme( $photon_url, $scheme );
 }
+
+/**
+ * Add an easy way to photon-ize a URL that is safe to call even if Jetpack isn't active.
+ *
+ * See: https://jetpack.com/2013/07/11/photon-and-themes/
+ */
 add_filter( 'jetpack_photon_url', 'jetpack_photon_url', 10, 3 );
 
 /**

load-jetpack.php

@@ -84,15 +84,6 @@ function jetpack_should_use_minified_assets() {
 add_filter( 'jetpack_static_url', array( 'Jetpack', 'staticize_subdomain' ) );
 add_filter( 'is_jetpack_site', '__return_true' );
 
-/**
- * Add an easy way to photon-ize a URL that is safe to call even if Jetpack isn't active.
- *
- * See: https://jetpack.com/2013/07/11/photon-and-themes/
- */
-if ( Jetpack::is_module_active( 'photon' ) ) {
-	add_filter( 'jetpack_photon_url', 'jetpack_photon_url', 10, 3 );
-}
-
 if ( JETPACK__SANDBOX_DOMAIN ) {
 	require_once JETPACK__PLUGIN_DIR . '_inc/jetpack-server-sandbox.php';
 }