Make logging cost free when there is no output target (#12247)

The logging streams now do almost no work when there is no output target for them.

For example, if LL_VERBOSE has no output targets, then `verbosestream << x` will return a StreamProxy with a null target. Any further `<<` operations applied to it will do nothing.

src/network/connection.cpp

@@ -41,25 +41,14 @@ namespace con
 /* defines used for debugging and profiling                                   */
 /******************************************************************************/
 #ifdef NDEBUG
-	#define LOG(a) a
 	#define PROFILE(a)
 #else
-	#if 0
-	/* this mutex is used to achieve log message consistency */
-	std::mutex log_message_mutex;
-	#define LOG(a)                                                                 \
-		{                                                                          \
-		MutexAutoLock loglock(log_message_mutex);                                 \
-		a;                                                                         \
-		}
-	#else
-	// Prevent deadlocks until a solution is found after 5.2.0 (TODO)
-	#define LOG(a) a
-	#endif
-
 	#define PROFILE(a) a
 #endif
 
+// TODO: Clean this up.
+#define LOG(a) a
+
 #define PING_TIMEOUT 5.0
 
 u16 BufferedPacket::getSeqnum() const