tools/bpftool: Replace bpf_program__title() with bpf_program__section_name()

bpf_program__title() is deprecated, switch to bpf_program__section_name() and
avoid compilation warnings.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200903203542.15944-9-andriin@fb.com