Remove broken test testRfc6724Sort

This test is conitnuely fail in cuttlefish.
Lack of ipv6 default route in cuttlefish caused the test failed.
The reason is that the result of rfc6724Sort depends on on the route in system.
It is not good to expect any route should exists, so remove it.

Bug: 133649648
Test: atest DnsUtilsTest
Change-Id: I91f89782b9b989fa1a49e666bb5ce2df3a0dbbf7