Simplifying away the progressKey

Simplifying away the progressKey

Simplifying away all the progressKey stuff gives exactly the same bench,
without any speed impact. Tested for speed against master with two benches
at depth 22 ran in parallel:

**testedpatch**
Total time (ms) : 92350
Nodes searched : 178962949
Nodes/second : 1937877

**master**
Total time (ms) : 92358
Nodes searched : 178962949
Nodes/second : 1937709

We also tested the patch at STC for no-regression with [-3, 1] bounds:

LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 57299 W: 11529 L: 11474 D: 34296
http://tests.stockfishchess.org/tests/view/5b015a1c0ebc5914abc126e5

Closes https://github.com/official-stockfish/Stockfish/pull/1603

No functional change.