Don't adjust MoveOverhead by increment

This is a change to address a potential timing issue for slow networks.

Move Overhead was limited by TC increment,
which might be problematic if small increments (or sudden death)
on slow networks (needing high Move Overhead) are used.

STC, sudden death.
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 169368 W: 38023 L: 38054 D: 93291
Ptnml(0-2): 3767, 20250, 36595, 20391, 3681
https://tests.stockfishchess.org/tests/view/5ebf25efe9d85f94dc42986f

STC, 10+0.1
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 83896 W: 16092 L: 16026 D: 51778
Ptnml(0-2): 1401, 9697, 19670, 9795, 1385
https://tests.stockfishchess.org/tests/view/5ec0239de9d85f94dc42991e

closes https://github.com/official-stockfish/Stockfish/pull/2684

No functional change.