Revert "Add the PHP ldap module as a requirement"

This reverts commit 8a4cbd4.

Author: tvdijen

composer.json

@@ -32,7 +32,6 @@
     },
     "require": {
         "php": ">=5.6",
-        "ext-ldap": "*",
         "simplesamlphp/composer-module-installer": "~1.1",
         "webmozart/assert": "~1.4"
     },