build: Remove message about Ubuntu 13.10 when no boost sleep implementation found

It's only confusing people into thinking that they should mess with
boost versions, which should not be necessary to get bitcoind to work.

If there is a bug in the build system with autodetecting boost it needs
to be solved not worked around.

configure.ac

@@ -577,7 +577,7 @@ CPPFLAGS="$TEMP_CPPFLAGS"
 fi
 
 if test x$boost_sleep != xyes; then
-  AC_MSG_ERROR(No working boost sleep implementation found. If on ubuntu 13.10 with libboost1.54-all-dev remove libboost.1.54-all-dev and use libboost1.53-all-dev)
+  AC_MSG_ERROR(No working boost sleep implementation found.)
 fi
 
 AC_ARG_WITH([utils],