phpdbg_clear() is documented, remove warning (#4638)

Author: DanielEScherzer

reference/phpdbg/functions/phpdbg-clear.xml

@@ -17,9 +17,6 @@
    Clear all breakpoints that have been set, either via one of the
    <function>phpdbg_break_*</function> functions or interactively in the console.
   </para>
-
-  &warn.undocumented.func;
-
  </refsect1>
 
  <refsect1 role="parameters">