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/connectionthreads.cpp

@@ -32,22 +32,18 @@ namespace con
 /* defines used for debugging and profiling                                   */
 /******************************************************************************/
 #ifdef NDEBUG
-#define LOG(a) a
 #define PROFILE(a)
 #undef DEBUG_CONNECTION_KBPS
 #else
 /* this mutex is used to achieve log message consistency */
-std::mutex log_conthread_mutex;
-#define LOG(a)                                                                \
-	{                                                                         \
-	MutexAutoLock loglock(log_conthread_mutex);                                 \
-	a;                                                                        \
-	}
 #define PROFILE(a) a
 //#define DEBUG_CONNECTION_KBPS
 #undef DEBUG_CONNECTION_KBPS
 #endif
 
+// TODO: Clean this up.
+#define LOG(a) a
+
 #define WINDOW_SIZE 5
 
 static session_t readPeerId(const u8 *packetdata)