samples, bpf: Refactor kprobe, tail call kern progs map definition

Because the previous two commit replaced the bpf_load implementation of
the user program with libbpf, the corresponding kernel program's MAP
definition can be replaced with new BTF-defined map syntax.

This commit only updates the samples which uses libbpf API for loading
bpf program not with bpf_load.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200516040608.1377876-6-danieltimlee@gmail.com