sleep-config: downgrade log level in can_s2h()

As in the previous commit: can_sleep() is more a library-style function,
hence log at debug level only.

src/shared/sleep-config.c

@@ -588,8 +588,7 @@ static bool can_s2h(const SleepConfig *sleep_config) {
         int r;
 
         if (!clock_supported(CLOCK_BOOTTIME_ALARM)) {
-                log_full(errno == ENOENT ? LOG_DEBUG : LOG_WARNING,
-                         "CLOCK_BOOTTIME_ALARM is not supported");
+                log_debug("CLOCK_BOOTTIME_ALARM is not supported.");
                 return false;
         }