Remove per thread instances of Endgames. (#2056)

Similar to PSQT we only need one instance of the Endgames resource. The current per thread copies are identical and read only(after initialization) so from a design point of view it doesn't make sense to have them.

Tested for no slowdown.
http://tests.stockfishchess.org/tests/view/5c94377a0ebc5925cfff43ca
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 17320 W: 3487 L: 3359 D: 10474

No functional change.

src/main.cpp

@@ -26,6 +26,7 @@
 #include "thread.h"
 #include "tt.h"
 #include "uci.h"
+#include "endgame.h"
 #include "syzygy/tbprobe.h"
 
 namespace PSQT {
@@ -42,6 +43,7 @@ int main(int argc, char* argv[]) {
   Position::init();
   Bitbases::init();
   Search::init();
+  Endgames::init();
   Threads.set(Options["Threads"]);
   Search::clear(); // After threads are up