General: revert [38467], wp_is_IE() should not exist.

See #37699.


git-svn-id: https://develop.svn.wordpress.org/trunk@38468 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/vars.php

@@ -139,15 +139,3 @@ function wp_is_mobile() {
 
 	return $is_mobile;
 }
-
-/**
- * @since 4.7.0
- *
- * @global bool $is_IE Whether the current user agent is Internet Explorer
- *
- * @return bool Return the value of the $is_IE global.
- */
-function wp_is_IE() {
-	global $is_IE;
-	return $is_IE;
-}