selftests/bpf: Retire test_sock.c

Completely remove test_sock.c and associated config.

Signed-off-by: Jordan Rife <jrife@google.com>
Link: https://lore.kernel.org/r/20241022152913.574836-5-jrife@google.com


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