Revert "Simplify En Passant"
This reverts commit 9f8058bd26df1c3ca37b85f811026f1eb82e6524.
Fixes the memory leak discussed in pull request #3523
https://github.com/official-stockfish/Stockfish/pull/3523
Passed non-regression STC:
LLR: 2.95 (-2.94,2.94) <-2.50,0.50>
Total: 76184 W: 6330 L: 6282 D: 63572
Ptnml(0-2): 202, 5047, 27564, 5059, 220
https://tests.stockfishchess.org/tests/view/60ba146c457376eb8bcaa2e2
closes https://github.com/official-stockfish/Stockfish/pull/3527
Benched to verify there is no functional change.
Bench: 4364128