routecache: Remove debugging printout

This removes the following debuggign printout from OSv boot that was
added in commit c9f3702 ("Route Cache patch #2"):

  routecache.hh: caching route for fea9fea9 ffffff

Reviewed-by: Asias He <asias@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>