ext/pcntl: Remove falseproblem banner for pcntl_setcpuaffinity (#5661)

The function can only return a boolean value, so the banner does not apply.

Author: SteenSchutt

reference/pcntl/functions/pcntl-setcpuaffinity.xml

@@ -46,7 +46,6 @@
   <simpara>
    &return.success;
   </simpara>
-  &return.falseproblem;
  </refsect1>
 
  <refsect1 role="errors">