libbpf 1.0: Deprecate bpf_object__find_map_by_offset() API

API created with simplistic assumptions about BPF map definitions.
It hasn’t worked for a while, deprecate it in preparation for
libbpf 1.0.

  [0] Closes: https://github.com/libbpf/libbpf/issues/302

Signed-off-by: Christy Lee <christylee@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220105003120.2222673-1-christylee@fb.com