selftests/bpf: Don't use deprecated libbpf APIs

Remove all uses of bpf_program__title() and
bpf_program__find_program_by_title().

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200903203542.15944-10-andriin@fb.com