small ttCapture simplification.

small ttCapture simplification.

ttCapture can be assigned to only once outside of the main loop. The patch seems
functional at higher depths (seems possible in the case of non-legal TTmoves that
are captures).

passed STC
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 23189 W: 5098 L: 4980 D: 13111
http://tests.stockfishchess.org/tests/view/5bb3822c0ebc592439f6d966

passed LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 10336 W: 1665 L: 1529 D: 7142
http://tests.stockfishchess.org/tests/view/5bb39a190ebc592439f6db8a

unchanged bench: 4312846