Customize: Remove unreachable return statements in WP_Customize_Manager.

This addresses 3 PHPStan errors:

> Unreachable statement - code above always terminates.

Each line of code is unreachable because the preceding statement exits execution.

Developed in WordPress#12497.
Follow-up to r62704.

Props soean, mukesh27.
See #64898.


git-svn-id: https://develop.svn.wordpress.org/trunk@62763 602fd350-edb4-49c9-b593-d223f7449a82

Author: westonruter

src/wp-includes/class-wp-customize-manager.php

@@ -1936,7 +1936,6 @@ public function customize_preview_init() {
 					'<code>customize_messenger_channel</code>'
 				)
 			);
-			return;
 		}
 
 		$this->prepare_controls();
@@ -3166,7 +3165,6 @@ public function handle_changeset_trash_request() {
 					'code'    => 'non_existent_changeset',
 				)
 			);
-			return;
 		}
 
 		if ( ! current_user_can( get_post_type_object( 'customize_changeset' )->cap->delete_post, $changeset_post_id ) ) {
@@ -3197,7 +3195,6 @@ public function handle_changeset_trash_request() {
 					'code'    => 'changeset_already_trashed',
 				)
 			);
-			return;
 		}
 
 		$r = $this->trash_changeset_post( $changeset_post_id );