[time.syn] Use "ymwd" parameter name consistently (#6029)

Author: mordante

source/time.tex

@@ -597,7 +597,7 @@
 
   template<class charT, class traits>
     basic_ostream<charT, traits>&
-      operator<<(basic_ostream<charT, traits>& os, const year_month_weekday& ymwdi);
+      operator<<(basic_ostream<charT, traits>& os, const year_month_weekday& ymwd);
 
   // \ref{time.cal.ymwdlast}, class \tcode{year_month_weekday_last}
   class year_month_weekday_last;