selftests/bpf: remove last tests with legacy BPF map definitions

selftests/bpf: remove last tests with legacy BPF map definitions

Libbpf 1.0 stops support legacy-style BPF map definitions. Selftests has
been migrated away from using legacy BPF map definitions except for two
selftests, to make sure that legacy functionality still worked in
pre-1.0 libbpf. Now it's time to let those tests go as libbpf 1.0 is
imminent.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220627211527.2245459-14-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>