Remove unnecessary Serial.begin()

Removes an unnecessary Serial.begin() that was left behind from debugging.

Former-commit-id: b848288

Author: alrvid

libraries/RTC/examples/RTC_PeriodicExample/RTC_PeriodicExample.ino

@@ -25,9 +25,6 @@ void periodicCallback()
 
 void setup() {
   pinMode(LED_BUILTIN, OUTPUT);
-
-  Serial.begin(9600);
-  while (!Serial) ;
 
   // Initialize the RTC
   RTC.begin();