Revert "Fix example of P/R"

This reverts commit 5f563b1.

Author: Dani-Hub

xml/issue4264.xml

@@ -216,7 +216,7 @@ void f2() noexcept;
 function_ref<void() noexcept> r1(&r1);
 function_ref<void()> r2(r1);
 r1 = &f2;
-r2(); // it is unspecified if `f1` or `f2` is invoked</ins>
+f2(); // it is unspecified if `f1` or `f2` is invoked</ins>
 </pre>
 <p> 
 <ins>&mdash; <i>end example</i>]</ins>