tools: bpftool: don't pass FEATURES_DUMP to libbpf

bpftool does not export features it probed for, i.e.
FEATURE_DUMP_EXPORT is always empty, so don't try to communicate
the features to libbpf.  It has no effect.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>