Revert "define digitalPinToInterrupt for backwards compatibility"

This reverts commit 5f3ee5b.

Author: sgbihu

cores/arduino/Arduino.h

@@ -43,8 +43,6 @@ extern "C"{
 #define clockCyclesToMicroseconds(a) ( ((a) * 1000L) / (SYSTEM_CORE_CLOCK / 1000L) )
 #define microsecondsToClockCycles(a) ( (a) * (SYSTEM_CORE_CLOCK / 1000000L) )
 
-#define digitalPinToInterrupt(P)   ( P )
-
 void yield(void);
 
 /* sketch */