Remove duplicated information from a few error messages.
Remove duplicated information from a few error messages.

* subversion/libsvn_subr/io.c
  (svn_io_wait_for_cmd): Remove 'exitwhy' from the error message for the cases
    where exitwhy is already completely handled by the specific error message.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1489935 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion