selftests/bpf: Fix resource leaks caused by missing cleanups

selftests/bpf: Fix resource leaks caused by missing cleanups

ASAN reported a number of resource leaks:
  - Add missing  *__destroy(skel) calls
  - Replace bpf_link__detach() with bpf_link__destroy() where appropriate
  - cgrp_local_storage: Add bpf_link__destroy() when bpf_iter_create fails
  - dynptr: Add missing bpf_object__close()

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260223190736.649171-16-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>