libbpf: Update the comment to remove the reference to the deprecated interface bpf_pr...

libbpf: Update the comment to remove the reference to the deprecated interface bpf_program__load().

Commit be2f2d1680df ("libbpf: Deprecate bpf_program__load() API") marked
bpf_program__load() as deprecated starting with libbpf v0.6. And later
in commit 146bf811f5ac ("libbpf: remove most other deprecated high-level
APIs") actually removed the bpf_program__load() implementation and
related old high-level APIs.

This patch update the comment in bpf_program__set_attach_target() to
remove the reference to the deprecated interface bpf_program__load().

Signed-off-by: Jianyun Gao <jianyungao89@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20251103120727.145965-1-jianyungao89@gmail.com