Strip throughput rates if all are `?`

[alexheretic]

Thanks for critcmp. My benches don't tend to have throughput figures, I get two columns of ? B/sec.

It's not the worst thing having them, but maybe these could be auto-stripped away when they're all ??

Example:

group                                                 master                                 new
-----                                                 ------                                 ---
no_cache_render_3_medium_sections_fully               1.29  1647.1±18.17µs        ? B/sec    1.00  1277.4±17.63µs        ? B/sec
no_cache_render_v_bottom_1_large_section_partially    1.62      7.6±0.02ms        ? B/sec    1.00      4.7±0.02ms        ? B/sec
no_cache_render_v_center_1_large_section_partially    1.66      7.7±0.02ms        ? B/sec    1.00      4.7±0.04ms        ? B/sec