make rule/all fails

[Citrullin]

make rule/all fails with the message

/bin/sh: 1: /home/citrullin/git/webthing-arduino/examples/LevelSensor/../../tmp/arduino-1.8.5/hardware/tools/avr/bin/avr-g++: not found

Since the project focuses on ESP32 (and MKR1000), we don't even need to make sure, if it compiles on AVR. 8-Bit is probably never going to be a target for this project. We can just remove it.