selftests/bpf: Stop using bpf_object__find_program_by_title API.

bpf_object__find_program_by_title is going to be deprecated.  Replace
all use cases in tools/testing/selftests/bpf with
bpf_object__find_program_by_name or bpf_object__for_each_program.

Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211214035931.1148209-2-kuifeng@fb.com