Add note that "logfile" is deprecated

docs/api.rst

@@ -296,10 +296,6 @@ Process Control
             Exit status (errorlevel) of process, or 0 if the process is still
             running.
 
-        .. describe:: logfile
-
-            Alias for "stdout_logfile".
-
         .. describe:: pid
 
             UNIX process ID (PID) of the process, or 0 if the process is not