Fixes the following cppcheck issues:
examples/SecretKnockSensor/SecretKnockSensor.ino
305 variableScope 398 style
The scope of the variable 'timeDiff' can be reduced.
examples/SensebenderGatewaySerial/SensebenderGatewaySerial.ino
127 variableScope 398 style
The scope of the variable 'led_state' can be reduced.
Removing MY_LED_BLINKING_FEATURE, as we now are
using MY_DEFAULT_LED_xx_PIN defines to enable
LED blinking feature.
updated Gateway sketches to not refer to
MY_LED_BLINKING_FEATURE any more
fixes#562