Update WatchdogAVR.cpp

[peter-scholtens]

My arduino IDE includes the file arduino-1.8.13/hardware/tools/avr/avr/include/avr/sleep.h which contains already a sleep_disable() call, see the definition below. So it can be removed? Or is this done differently in the various boards?

#define sleep_mode() \
do {                 \
    sleep_enable();  \
    sleep_cpu();     \
    sleep_disable(); \
} while (0)```