route.8: Don't reference an external command in EXAMPLES

It is better to mention the externel command for showing
the routing table as using an explicit command.

PR: 231579
Suggested by: karels
Reviewed by: karles, gbe
Differential Revision: https://reviews.freebsd.org/D39075

(cherry picked from commit 21f268182838f072f96234c727778d5603a580e3)