[components] remove libc dependency in ulog and RTC driver.

components/drivers/Kconfig

@@ -125,7 +125,6 @@ config RT_USING_PM
 
 config RT_USING_RTC
     bool "Using RTC device drivers"
-    select RT_USING_LIBC
     default n
 
     if RT_USING_RTC

components/utilities/Kconfig

@@ -146,7 +146,6 @@ config RT_USING_ULOG
             config ULOG_TIME_USING_TIMESTAMP
                 bool "Enable timestamp format for time."
                 default n
-                select RT_USING_LIBC
                 depends on ULOG_OUTPUT_TIME
 
             config ULOG_OUTPUT_LEVEL