Further tweak movecount pruning

Passed both short TC
LLR: 2.95 (-2.94,2.94)
Total: 15140 W: 3125 L: 2976 D: 9039

And long TC
LLR: 2.95 (-2.94,2.94)
Total: 17118 W: 3165 L: 2974 D: 10979

bench: 4132374
Merge remote-tracking branch 'upstream/master' into AlwaysDancing