Remove Redundant file.close()
In `Benchmark::setup_bench()`, the `std::ifstream file(fenFile);` object is declared with local scope inside an `else` block. Right before the block terminates, `file.close()` is called explicitly.
Because `std::ifstream` follows RAII semantics, its destructor automatically flushes and closes the underlying file descriptor when the stream goes out of scope. The manual `file.close()` call is therefore redundant.
closes https://github.com/official-stockfish/Stockfish/pull/7190
No functional change