don't run ThreadMessageHandler at lowered priority

There's no clear reason ThreadMessageHandler should be low priority.
Fixes #8010 (priority inversion).

src/util.cpp

@@ -811,19 +811,6 @@ bool SetupNetworking()
     return true;
 }
 
-void SetThreadPriority(int nPriority)
-{
-#ifdef WIN32
-    SetThreadPriority(GetCurrentThread(), nPriority);
-#else // WIN32
-#ifdef PRIO_THREAD
-    setpriority(PRIO_THREAD, 0, nPriority);
-#else // PRIO_THREAD
-    setpriority(PRIO_PROCESS, 0, nPriority);
-#endif // PRIO_THREAD
-#endif // WIN32
-}
-
 int GetNumCores()
 {
 #if BOOST_VERSION >= 105600