traceroute tests: fix the test when SCTP is supported

The SCTP test assumes a default system configuration where SCTP is not
supported, so the probe packet returns an ICMP error which is displayed
as a !P response. If SCTP is supported, then something else is returned
instead (depending on exactly what probe we sent, but not an ICMP error)
and the test fails.

Since we already check the correct probes are sent using tcpdump, remove
the match for the second hop entirely.

Reported by: Jenkins
Reviewed by: des
Approved by: des (mentor)
Differential Revision: https://reviews.freebsd.org/D50336