esp32/machine_uart: Remove UART event queue object.
esp32/machine_uart: Remove UART event queue object.

This event queue has UART events posted to it and they need to be drained
for it to operate without error.  The queue is not used by the uPy UART
class so it should be removed to prevent the IDF emitting errors.

Fixes #3704.

pozetroninc/micropython,swegener/micropython,kerneltask/micropython,kerneltask/micropython,ryannathans/micropython,pozetroninc/micropython,swegener/micropython,pramasoul/micropython,selste/micropython,MrSurly/micropython,tobbad/micropython,pozetroninc/micropython,tobbad/micropython,swegener/micropython,MrSurly/micropython,ryannathans/micropython,henriknelson/micropython,pozetroninc/micropython,bvernoux/micropython,selste/micropython,trezor/micropython,bvernoux/micropython,pramasoul/micropython,tobbad/micropython,pfalcon/micropython,selste/micropython,henriknelson/micropython,pramasoul/micropython,tralamazza/micropython,pfalcon/micropython,bvernoux/micropython,tralamazza/micropython,pfalcon/micropython,adafruit/micropython,selste/micropython,adafruit/micropython,MrSurly/micropython,trezor/micropython,pramasoul/micropython,dmazzella/micropython,adafruit/micropython,MrSurly/micropython,pfalcon/micropython,adafruit/circuitpython,adafruit/circuitpython,MrSurly/micropython,ryannathans/micropython,bvernoux/micropython,adafruit/circuitpython,tobbad/micropython,adafruit/micropython,ryannathans/micropython,trezor/micropython,kerneltask/micropython,swegener/micropython,dmazzella/micropython,adafruit/circuitpython,pfalcon/micropython,kerneltask/micropython,adafruit/circuitpython,bvernoux/micropython,selste/micropython,henriknelson/micropython,dmazzella/micropython,trezor/micropython,kerneltask/micropython,dmazzella/micropython,pramasoul/micropython,tralamazza/micropython,henriknelson/micropython,pozetroninc/micropython,ryannathans/micropython,adafruit/circuitpython,tralamazza/micropython,tobbad/micropython,adafruit/micropython,trezor/micropython,swegener/micropython,henriknelson/micropython