sched/clock: Remove CLOCK_MONOTONIC option from Kconfig

here is the reason:
1.clock_systime_timespec(core function) always exist regardless the setting
2.CLOCK_MONOTONIC is a foundamental clock type required by many places

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

drivers/sensors/bmp280.c

@@ -643,11 +643,7 @@ static int bmp280_fetch(FAR struct sensor_lowerhalf_s *lower,
   temp = bmp280_compensate_temp(priv, temp);
   press = bmp280_compensate_press(priv, press);
 
-#ifdef CONFIG_CLOCK_MONOTONIC
   clock_gettime(CLOCK_MONOTONIC, &ts);
-#else
-  clock_gettime(CLOCK_REALTIME, &ts);
-#endif
 
   baro_data.timestamp = 1000000ull * ts.tv_sec + ts.tv_nsec / 1000;
   baro_data.pressure = press / 100.0f;

drivers/sensors/ds18b20.c

@@ -549,12 +549,8 @@ static int ds18b20_set_alarm(FAR struct ds18b20_dev_s *dev,
 static unsigned long ds18b20_curtime(void)
 {
   struct timespec ts;
-#ifdef CONFIG_CLOCK_MONOTONIC
-  clock_gettime(CLOCK_MONOTONIC, &ts);
-#else
-  clock_gettime(CLOCK_REALTIME, &ts);
-#endif
 
+  clock_gettime(CLOCK_MONOTONIC, &ts);
   return 1000000ull * ts.tv_sec + ts.tv_nsec / 1000;
 }
 

drivers/sensors/hyt271.c

@@ -187,12 +187,8 @@ static void hyt271_temp_from_rawdata(FAR struct hyt271_sensor_data_s *data,
 static unsigned long hyt271_curtime(void)
 {
   struct timespec ts;
-#ifdef CONFIG_CLOCK_MONOTONIC
-  clock_gettime(CLOCK_MONOTONIC, &ts);
-#else
-  clock_gettime(CLOCK_REALTIME, &ts);
-#endif
 
+  clock_gettime(CLOCK_MONOTONIC, &ts);
   return 1000000ull * ts.tv_sec + ts.tv_nsec / 1000;
 }
 

drivers/sensors/lis2dh.c

@@ -1667,11 +1667,7 @@ static int lis2dh_reboot(FAR struct lis2dh_dev_s *dev)
 
   /* Prefer monotonic for timeout calculation when enabled. */
 
-#ifdef CONFIG_CLOCK_MONOTONIC
   clock_gettime(CLOCK_MONOTONIC, &start);
-#else
-  clock_gettime(CLOCK_REALTIME, &start);
-#endif
 
   /* Reboot to reset chip. */
 
@@ -1696,11 +1692,7 @@ static int lis2dh_reboot(FAR struct lis2dh_dev_s *dev)
           break;
         }
 
-#ifdef CONFIG_CLOCK_MONOTONIC
       clock_gettime(CLOCK_MONOTONIC, &curr);
-#else
-      clock_gettime(CLOCK_REALTIME, &curr);
-#endif
 
       diff_msec = (curr.tv_sec - start.tv_sec) * 1000;
       diff_msec += (curr.tv_nsec - start.tv_nsec) / (1000 * 1000);

drivers/sensors/ms5611.c

@@ -157,12 +157,8 @@ static const struct sensor_ops_s g_sensor_ops =
 static unsigned long ms5611_curtime(void)
 {
   struct timespec ts;
-#ifdef CONFIG_CLOCK_MONOTONIC
-  clock_gettime(CLOCK_MONOTONIC, &ts);
-#else
-  clock_gettime(CLOCK_REALTIME, &ts);
-#endif
 
+  clock_gettime(CLOCK_MONOTONIC, &ts);
   return 1000000ull * ts.tv_sec + ts.tv_nsec / 1000;
 }
 

drivers/syslog/vsyslog.c

@@ -105,17 +105,12 @@ int nx_vsyslog(int priority, FAR const IPTR char *fmt, FAR va_list *ap)
 
       clock_gettime(CLOCK_REALTIME, &ts);
 
-#elif defined(CONFIG_CLOCK_MONOTONIC)
+#else
       /* Prefer monotonic when enabled, as it can be synchronized to
        * RTC with clock_resynchronize.
        */
 
       clock_gettime(CLOCK_MONOTONIC, &ts);
-
-#else
-      /* Otherwise, fall back to the system timer */
-
-      clock_systime_timespec(&ts);
 #endif
 
       /* Prepend the message with the current time, if available */