Use compiler name lookup to simplify code

We don't need different names between a function and a
template. Compiler will know when use one or the other.

This let use restore original count_1s_xx() names instead of
sw_count_1s_xxx so to simplify a bit the code.

No functional change.

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

src/bitboard.cpp

@@ -461,7 +461,7 @@ namespace {
 
 
   Bitboard index_to_bitboard(int index, Bitboard mask) {
-    int i, j, bits = count_1s<false>(mask);
+    int i, j, bits = count_1s(mask);
     Bitboard result = 0ULL;
     for(i = 0; i < bits; i++) {
       j = pop_1st_bit(&mask);