fix: allow exit()

Author: astratagem

Kleinweb/ruleset.xml

@@ -91,7 +91,6 @@ them to our own mu-plugin or standard library.
                 <element key="die" value="null"/>
                 <element key="error_log" value="null"/>
                 <element key="eval" value="null"/>
-                <element key="exit" value="null"/>
                 <element key="extract" value="null"/>
                 <element key="goto" value="null"/>
                 <element key="ini_set" value="null"/>