array_walk: Fix misleading wording (#4960)

Since PHP8 this is no longer a warning but an actual exception.
Throw was never really right in the first place however, as warnings
are _emitted_, not _thrown_.

Author: ndossche

reference/array/functions/array-walk.xml

@@ -56,7 +56,7 @@
       <note>
         <para>
           Many internal functions (for example <function>strtolower</function>)
-          will throw a warning if more than the expected number of argument
+          will throw if more than the expected number of arguments
           are passed in and are not usable directly as a
           <parameter>callback</parameter>.
         </para>