boost: remove useless threadGroup parameter from Discover

src/init.cpp

@@ -1667,7 +1667,7 @@ bool AppInitMain()
     if (gArgs.GetBoolArg("-listenonion", DEFAULT_LISTEN_ONION))
         StartTorControl(threadGroup, scheduler);
 
-    Discover(threadGroup);
+    Discover();
 
     // Map ports with UPnP
     if (gArgs.GetBoolArg("-upnp", DEFAULT_UPNP)) {

src/net.cpp

@@ -2129,7 +2129,7 @@ bool CConnman::BindListenPort(const CService &addrBind, std::string& strError, b
     return true;
 }
 
-void Discover(boost::thread_group& threadGroup)
+void Discover()
 {
     if (!fDiscover)
         return;

src/net.h

@@ -37,10 +37,6 @@
 class CScheduler;
 class CNode;
 
-namespace boost {
-    class thread_group;
-} // namespace boost
-
 /** Time between pings automatically sent out for latency probing and keepalive (in seconds). */
 static const int PING_INTERVAL = 2 * 60;
 /** Time after which to disconnect, after waiting for a ping response (or inactivity). */
@@ -441,7 +437,7 @@ private:
     friend struct CConnmanTest;
 };
 extern std::unique_ptr<CConnman> g_connman;
-void Discover(boost::thread_group& threadGroup);
+void Discover();
 void StartMapPort();
 void InterruptMapPort();
 void StopMapPort();