Micro-optimze extension()

Explicitly write the conditions for pawn to 7th
and passed pawn instead of wrapping in redundant
helpers.

Also retire the now unused move_is_pawn_push_to_7th()
and the never used move_was_passed_pawn_push() and
move_is_deep_pawn_push()

Function extension() is so time critical that this
simple patch speeds up the pgo compile of 0.5% and
it is also more clear what actually happens there.

No functional change.

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

src/search.cpp

@@ -2267,12 +2267,13 @@ namespace {
 
     if (pos.type_of_piece_on(move_from(m)) == PAWN)
     {
-        if (pos.move_is_pawn_push_to_7th(m))
+        Color c = pos.side_to_move();
+        if (relative_rank(c, move_to(m)) == RANK_7)
         {
             result += PawnPushTo7thExtension[pvNode];
             *dangerous = true;
         }
-        if (pos.move_is_passed_pawn_push(m))
+        if (pos.pawn_is_passed(c, move_to(m)))
         {
             result += PassedPawnExtension[pvNode];
             *dangerous = true;