selftests/bpf: Migrate BPF_CGROUP_INET_SOCK_CREATE test cases to prog_tests

Move the "load w/o expected_attach_type" test case to
prog_tests/sock_create.c and drop the remaining test case, as it is made
redundant with the existing coverage inside prog_tests/sock_create.c.

Signed-off-by: Jordan Rife <jrife@google.com>
Link: https://lore.kernel.org/r/20241022152913.574836-4-jrife@google.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>