remove old easypost lib

Author: dleffler

install/upgrades/remove_oldfiles.php

@@ -688,6 +688,7 @@ function upgrade() {
             'external/easypost-php-6.2.0/',
             'external/easypost-php-6.3.0/',
             'external/easypost-php-6.6.0/',
+            'external/easypost-php-7.4.2/',
             'external/editors/connector/',
             'external/editors/FCKeditor/',
             'external/editors/ckeditor/images',