Remove by-reference from wp_remote_retrieve_* functions

[nacin]

See #27656 for explanation, reasoning, concerns, etc.

[jesin]

Is that the right patch?

# grep -r 'function wp_remote_retrieve' .

./wp-includes/http.php:function wp_remote_retrieve_headers(&$response) {
./wp-includes/http.php:function wp_remote_retrieve_header(&$response, $header) {
./wp-includes/http.php:function wp_remote_retrieve_response_code(&$response) {
./wp-includes/http.php:function wp_remote_retrieve_response_message(&$response) {
./wp-includes/http.php:function wp_remote_retrieve_body(&$response) {

[wonderboymusic]

In 28257:

Remove by-reference modifiers from arguments in wp_remote_retrieve_* functions.

Props jesin.
Fixes #27687.