Retire grain size code

Seems useless at long TC.

Tested at 60+0.05
ELO: 2.98 +-2.2 (95%) LOS: 99.6%
Total: 30440 W: 4934 L: 4673 D: 20833

And at 120+0.05
ELO: 2.50 +-2.6 (95%) LOS: 97.1%
Total: 19633 W: 2848 L: 2707 D: 14078

bench: 8502826