[RFCLAT#8] clatd_test: remove or refactor tests for configure_clat_ipv6_address

1. Delete the test because it has been moved to netd.
- ConfigureIpv6Address

2. Refactor the existing test.
Assign IPv6 address directly because the address is applied by
cli argument now because configure_clat_ipv6_address() is
removed.
- Ipv6AddressChanged

Bug: 212345928
Test: atest clatd_test

Change-Id: I673327a36727e22f4ab23c191ee389fc1914016c
1 file changed