It looks like you are using JetPack’s Photon which adds query strings to your URLs. According to this thread there is no way to remove them https://wordpress.org/support/topic/how-to-remove-photon-query-string?replies=2
If you want to get rid of the query strings I would suggest deactivating photon, using a CDN which does not add query strings, and using the snippet you mentioned:
function _remove_script_version( $src ){
$parts = explode( '?ver', $src );
return $parts[0];
}
add_filter( 'script_loader_src', '_remove_script_version', 15, 1 );
add_filter( 'style_loader_src', '_remove_script_version', 15, 1 );