Revert "add (hidden) _NGINX_XACCEL_PREFIX which uses nginx X-Accel-Redirect to serve static files faster"

This reverts commit c5c3a0a2a8.

include/functions.php

@@ -2619,13 +2619,7 @@
 			$stamp = gmdate("D, d M Y H:i:s", filemtime($filename)) . " GMT";
 			header("Last-Modified: $stamp", true);
 
-			if (defined('_NGINX_XACCEL_PREFIX') && _NGINX_XACCEL_PREFIX) {
+			return readfile($filename);
-				header("X-Accel-Redirect: " . _NGINX_XACCEL_PREFIX . "/" . $filename);
-
-				return false;
-			} else {
-				return readfile($filename);
-			}
 		} else {
 			return false;
 		}