fix(migration84/deprecated): duplicate word (#3995)

Author: KentarouTakeda

appendices/migration84/deprecated.xml

@@ -294,7 +294,7 @@ class _MyClass {}
    are now deprecated.
    If this functionality is needed a SQL <literal>FLUSH</literal> command
    can be used instead.
-   All <constant>All MYSQLI_REFRESH_<replaceable>*</replaceable></constant>
+   All <constant>MYSQLI_REFRESH_<replaceable>*</replaceable></constant>
    constants have been deprecated as well.
   </simpara>