tools/bpftool: Remove warning about PID iterator support

Don't emit warning that bpftool was built without PID iterator support. This
error garbles JSON output of otherwise perfectly valid show commands.

Reported-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200710232605.20918-1-andriin@fb.com

tools/bpf/bpftool/pids.c

@@ -15,7 +15,6 @@
 
 int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
 {
-	p_err("bpftool built without PID iterator support");
 	return -ENOTSUP;
 }
 void delete_obj_refs_table(struct obj_refs_table *table) {}