…ockfish#1915)

The extra condition is used as a shortcut to skip the following 3 assignments:

```C++
        Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
        Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
        Bitboard b3 = shift<Up     >(pawnsOn7) & emptySquares;
```

In case of EVASION with no target on 8th rank (the common case), we end up performing the 3 statements for nothing because b1 = b2 = b3 = 0.

But this is just a small micro-optimization and the condition is quite confusing, so just remove it and prefer a readable code instead.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 78020 W: 16978 L: 16967 D: 44075
http://tests.stockfishchess.org/tests/view/5c27b4fe0ebc5902ba135bb0

No functional change.

This custom predicate filter creates an unnecessary abstraction layer, but doesn't make the code any more readable. The code is clear enough without it.

No functional change.

A single popcount in evaluate.cpp replaces all openFiles stuff in pawns. It doesn't seem to affect performance at all.

STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 28103 W: 6134 L: 6025 D: 15944
http://tests.stockfishchess.org/tests/view/5b7d70a20ebc5902bdbb1999

No functional change.

To address official-stockfish#1862

No functional change.