Revert setting a flag when TT value equals static evaluation

Revert setting a flag when TT value equals static evaluation
Strangely enough it seems that optimization doesn't work.

After 760 games at 1+0: +155 -184 =421 -13 ELO

Probably the overhead, although small, for setting the flag
is not compensated by the saved evaluation call.

This could be due to the fact that after a TT value is stored,
if and when we hit the position again the stored TT value is
actually used as a cut-off so that we don't need to go on
with another search and evaluation is avoided in any case.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>