bpf: sockmap, remove samples program

The BPF sample sockmap is redundant now that equivelant tests exist
in the BPF selftests. Lets remove this sample and only keep the
selftest version that will be run as part of the selftest suite.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>