tests/harness/fdtracker.cc: Don't report apparent leaks of fds
opened on /dev/urandom - at least on Linux, something in the C
library seems to lazily open it, and the report of a possible leak
followed by assurance that it's OK really is just noise we could
do without.

git-svn-id: file:///home/xapian-svn/xapian/trunk@18243 6b2f1b92-a4f3-0310-943f-de3cbe41748b