libbpf: cleanup LIBBPF_DEPRECATED_SINCE supporting macros for v0.x

Keep the LIBBPF_DEPRECATED_SINCE macro "framework" for future
deprecations, but clean up 0.x related helper macros.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220627211527.2245459-11-andrii@kernel.org


Signed-off-by: Alexei Starovoitov <ast@kernel.org>