Code Modernization: Remove unnecessary reference sign from get_comment() definition.

This fixes a PHP 8 "argument must be passed by reference, value given" error when using `array_map( 'get_comment', ... )`.

Object variables in PHP 5+ contain a reference to the object, and it's the reference that's passed around.

Note: This reverts [48838], which is now redundant.

Follow-up to a similar change for `get_post()` in [21572].

See #50913.

git-svn-id: https://develop.svn.wordpress.org/trunk@48961 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment.php

@@ -192,7 +192,7 @@ function get_approved_comments( $post_id, $args = array() ) {
  *                                       respectively. Default OBJECT.
  * @return WP_Comment|array|null Depends on $output value.
  */
-function get_comment( &$comment = null, $output = OBJECT ) {
+function get_comment( $comment = null, $output = OBJECT ) {
 	if ( empty( $comment ) && isset( $GLOBALS['comment'] ) ) {
 		$comment = $GLOBALS['comment'];
 	}