General: Remove the Pragma header from responses.

`Pragma` is supposed to be a request header, but we've been including it in responses since the beginning of time.

This is a relic dating all the way back to b2, probably originally added because Internet Explorer version 5 and earlier didn't understand the `Cache-Control` header in responses, but they did (incorrectly) obey the `Pragma` header.

Internet Explorer 6 and 7 will obey the `Pragma` response header only if no other cache-related response headers are present (in our case, they are always present), and all other browsers ignore the `Pragma` response header.

Props geekysoft.
Fixes #37250.



git-svn-id: https://develop.svn.wordpress.org/trunk@37944 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -1099,7 +1099,6 @@ function wp_get_nocache_headers() {
 	$headers = array(
 		'Expires' => 'Wed, 11 Jan 1984 05:00:00 GMT',
 		'Cache-Control' => 'no-cache, must-revalidate, max-age=0',
-		'Pragma' => 'no-cache',
 	);
 
 	if ( function_exists('apply_filters') ) {
@@ -1115,7 +1114,6 @@ function wp_get_nocache_headers() {
 		 *
 		 *     @type string $Expires       Expires header.
 		 *     @type string $Cache-Control Cache-Control header.
-		 *     @type string $Pragma        Pragma header.
 		 * }
 		 */
 		$headers = (array) apply_filters( 'nocache_headers', $headers );