The cranks now need a good scrub with a green Scotch pad in hot soapy water. It looks like most of that scale will scrub off, because I can scrape it off with my thumb nail. Then a light polish with Autosol might be all they need.
I don’t seem to be able to find a 16mm pedal wrench which looks like it’ll be up to the job, so I’m tempted to take the pedals off the spindles and leave them be. I don’t really need to take them out. That said, I will need to use a bench vice at work to free the drive-side bottom bracket cup, so I could clamp the pedal axles between a couple of bits of square section steel to free them.