selftests/bpf: lwt_seg6local: Remove unused routes

Some routes in fb00:: are initialized during setup, even though they
aren't needed by the test as the UDP packets will travel through the
lightweight tunnels.

Remove these unnecessary routes.

Signed-off-by: Bastien Curutchet (eBPF Foundation) <bastien.curutchet@bootlin.com>
Link: https://lore.kernel.org/r/20250307-seg6local-v1-1-990fff8f180d@bootlin.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>