Simplify futility_move_count
This patch reverts changes from #4032 which was introduced as a speedup.
Modern compilers no longer use DIV/IDIV instructions, potentially making
the explicit branch perform worse. Since evaluations spend significantly
more time now, the impact of the speedup in search diminishes with old
compilers as well.
GCC 14.1.0 profile-build, x86-64-vnni512
```
.text:000000014010FEA9 mov ecx, [rsp+3FB8h+var_3F5C]
...
.text:000000014010FEBD mov r10d, ecx
.text:000000014010FEC0 imul r10d, ecx
.text:000000014010FEC4 mov ecx, dword ptr [rsp+3FB8h+var_3F44+4]
.text:000000014010FEC8 add r10d, 3
.text:000000014010FECC mov r11d, r10d
.text:000000014010FECF sar r11d, 1
.text:000000014010FED2 cmp [rsp+3FB8h+var_3EE7], 0
.text:000000014010FEDA cmovnz r11d, r10d
```
LLVM 18.1.18 profile-build, x86-64-vnni512
```
.text:0000000140001EDC mov [rsp+40h+arg_E0], r13
.text:0000000140001EE4 movsxd rcx, r13d
.text:0000000140001EE7 mov rax, rcx
.text:0000000140001EEA mov [rsp+40h+arg_B8], rcx
.text:0000000140001EF2 imul eax, eax
.text:0000000140001EF5 add eax, 3
.text:0000000140001EF8 mov ecx, [rsp+40h+arg_8C]
.text:0000000140001EFF shrx eax, eax, ecx
.text:0000000140001F04 mov [rsp+40h+arg_190], rax
```
Passed non-regression STC:
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 109504 W: 28420 L: 28280 D: 52804
Ptnml(0-2): 355, 12326, 29273, 12420, 378
https://tests.stockfishchess.org/tests/view/6690dc095034141ae599c5fe
closes https://github.com/official-stockfish/Stockfish/pull/5478
No functional change