Retire quietsSearched[]

Use MovePicker moves[] to access already tried
quiet moves. A bit of care shall be taken
to avoid calling stage_moves() when we are still
at ttMove stage, because moves are yet to be
generated. Actually our staging move generation
makes this code a bit more tricky than what I'd
like, but removing an ausiliary redundant
array like quietsSearched[] is a good thing.

Idea by DiscoCheck

bench: 9355734
Fix an assert in SMP case

SMP case is very tricky and raises an assert in stage_moves():

assert(stage == KILLERS_S1 || stage == QUIETS_1_S1 || stage == QUIETS_2_S1)

So rewrite the code to just return moves[] when we are sure
we are in quiet moves stages.

Also rename stage_moves to quiet_moves to reflect that.

No functional change (but needs testing in SMP case)
Revert previous patch

It seems a regression at 15+0.05:
ELO: -4.82 +-2.1 (95%) LOS: 0.0%
Total: 40000 W: 7181 L: 7736 D: 25083

bench: 8331357
Get correct excluded moves for split nodes

Tested setting FakeSplit to true and running

./stockfish bench 128 2

There is a different signature with and without
the patch so it affects functionality but
only in SMP case.

bench: 8331357
Revert previous fix

It seems to intorduce a regression when tested
with 3 threads at 15+0.05:

ELO: -2.26 +-2.2 (95%) LOS: 2.4%
Total: 30000 W: 4813 L: 5008 D: 20179

bench: 8331357