one-shot logger updates

On one-shot second and further calls of one-shot message, no output was
producet, yet empty buffer was submitted to Log_output resulting in
false repeate messages:

    Last message repeated <n> times

To simplify the stuff, C++ API was removed and in the C API the Logger
is taken only if actual message will be output. If someone is willing to
use the C++ API, it can be later readded (not really needed now, only
simple message are presented).

src/debug.cpp

@@ -141,10 +141,11 @@ void log_msg(int level, const char *format, ...) {
 }
 
 void log_msg_once(int level, uint32_t id, const char *msg) {
-        if (log_level < level) {
+        if (Logger::oneshot_messages.count(id) > 0 || log_level < level) {
                 return;
         }
-        Logger(level).once(id, msg);
+        Logger::oneshot_messages.insert(id);
+        Logger(level).Get() << msg;
 }
 
 /**