Revert evaluation drift

Still not clear if it helps and, especially, how it
helps. So revert for now to avoid any influence on
future feature now under test.

With this patch we come back to be functional
equivalent to patch e33c94883 F_53.

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

src/search.cpp

@@ -1540,10 +1540,10 @@ namespace {
         // Use the cached evaluation score if possible
         assert(ei.futilityMargin == Value(0));
 
-        staticValue = tte->value() + 7;
+        staticValue = tte->value();
     }
     else
-        staticValue = evaluate(pos, ei, threadID) + 7;
+        staticValue = evaluate(pos, ei, threadID);
 
     if (ply == PLY_MAX - 1)
         return evaluate(pos, ei, threadID);