If log manager not inited messages are written to stdout.

If the log manager has not been inited, then messages are written
to stdout. In practice this can happen if something is directly or
indirectly logged during the startup of maxscale, before
skygw_logmanager_init() has been called. Some refactoring is needed
to allow skygw_logmanager_init() to be called very early at program
startup.

log_manager/log_manager.h

@@ -183,8 +183,6 @@ int skygw_log_get_augmentation();
 
 EXTERN_C_BLOCK_END
 
-const char* get_logpath_default(void);
-
 /**
  * Helper, not to be called directly.
  */