Unnecessary removal of ep square, may actually be decreasing performance

When stripping the ep square from FEN's when there is no ep capture possible, it causes an unnecessary disparity between positions/FENs generated from the new root position.  Although this doesn't affect functionality of the engine when used via UCI protocol, it can cause some issues with custom implementations of the engine.

For example, I wanted to compare the root FEN of the best move returned by search to the input FEN I sent via a custom harness I'm building. I was encountering FEN mismatches since the ep square from the input FEN was missing from the engine output. This issue also manifests itself currently in the engine's search log and other debugging functions.

I assumed that doing the capture checks had some downstream effect on search performance.  I conducted a benchmark test with the capture check removed and one with its current code. I saw no performance loss with the change, in fact, performance was slightly higher.  I imagine if I ran the comparison multiple times for each scenario and averaged the results of each, there would be no significant difference.

### Original code:
```
===========================
Total time (ms) : 5601
Nodes searched  : 6921356
Nodes/second    : 1235735
```

### After change:
```
===========================
Total time (ms) : 5401
Nodes searched  : 6921356
Nodes/second    : 1281495
```