selftests/bpf: Remove redundant sendmsg test cases

Remove these test cases completely, as the same behavior is already
covered by other sendmsg* test cases in prog_tests/sock_addr.c. This
just rewrites the destination address similar to sendmsg_v4_prog and
sendmsg_v6_prog.

Signed-off-by: Jordan Rife <jrife@google.com>
Link: https://lore.kernel.org/r/20240510190246.3247730-13-jrife@google.com


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