Remove global TB variables from search.cpp

Follow up cleanup of #4968, removes the global variables from search and
instead uses a dedicated tb config struct.

closes https://github.com/official-stockfish/Stockfish/pull/4982

No functional change

src/search.h

@@ -29,6 +29,7 @@
 #include "misc.h"
 #include "movepick.h"
 #include "position.h"
+#include "syzygy/tbprobe.h"
 #include "timeman.h"
 #include "types.h"
 
@@ -48,7 +49,6 @@ class UCI;
 
 namespace Search {
 
-
 // Stack struct keeps track of the information we need to remember from nodes
 // shallower and deeper in the tree during the search. Each search thread has
 // its own array of Stack objects, indexed by the current ply.
@@ -238,6 +238,8 @@ class Worker {
     // The main thread has a SearchManager, the others have a NullSearchManager
     std::unique_ptr<ISearchManager> manager;
 
+    Tablebases::Config tbConfig;
+
     const OptionsMap&   options;
     ThreadPool&         threads;
     TranspositionTable& tt;