tools: On shutdown no need to flush from tools/frr.in script

tools: On shutdown no need to flush from tools/frr.in script

Zebra already flushes routes on proper shutdown if you are not
using the -K option.  If you are using the -K option then you
do not want the tools/frr script to flush routes.

If zebra crashes and we restart then load up will either delete
the routes or leave them depending on the -K option.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>