Attempt to get rid of _isFollowingPV and _isScoringPV

[eduherminio]

First attempt: https://github.com/lynx-chess/Lynx/pull/311/files

Score of Lynx-remove-is-following-is-scoring-pv-1891-win-x64 vs Lynx 1875 - main: 555 - 657 - 985  [0.477] 2197
...      Lynx-remove-is-following-is-scoring-pv-1891-win-x64 playing White: 405 - 185 - 508  [0.600] 1098
...      Lynx-remove-is-following-is-scoring-pv-1891-win-x64 playing Black: 150 - 472 - 477  [0.354] 1099
...      White vs Black: 877 - 335 - 985  [0.623] 2197
Elo difference: -16.1 +/- 10.8, LOS: 0.2 %, DrawRatio: 44.8 %
SPRT: llr -2.25 (-78.0%), lbound -2.25, ubound 2.89 - H0 was accepted