don't run ThreadMessageHandler at lowered priority

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

src/compat.h

@@ -79,17 +79,6 @@ typedef u_int SOCKET;
 #define MSG_NOSIGNAL 0
 #endif
 
-#ifndef WIN32
-// PRIO_MAX is not defined on Solaris
-#ifndef PRIO_MAX
-#define PRIO_MAX 20
-#endif
-#define THREAD_PRIORITY_LOWEST          PRIO_MAX
-#define THREAD_PRIORITY_BELOW_NORMAL    2
-#define THREAD_PRIORITY_NORMAL          0
-#define THREAD_PRIORITY_ABOVE_NORMAL    (-2)
-#endif
-
 #if HAVE_DECL_STRNLEN == 0
 size_t strnlen( const char *start, size_t max_len);
 #endif // HAVE_DECL_STRNLEN