py/grammar: Remove unused rule.
py/grammar: Remove unused rule.

Since the recent changes to string/bytes literal concatenation, this rule
is no longer used.

micropython/micropython-esp32,dmazzella/micropython,bvernoux/micropython,swegener/micropython,blazewicz/micropython,MrSurly/micropython,blazewicz/micropython,cwyark/micropython,adafruit/circuitpython,pfalcon/micropython,toolmacher/micropython,AriZuu/micropython,swegener/micropython,kerneltask/micropython,MrSurly/micropython,blazewicz/micropython,MrSurly/micropython,infinnovation/micropython,puuu/micropython,henriknelson/micropython,PappaPeppar/micropython,HenrikSolver/micropython,lowRISC/micropython,Timmenem/micropython,dmazzella/micropython,kerneltask/micropython,swegener/micropython,toolmacher/micropython,micropython/micropython-esp32,torwag/micropython,alex-robbins/micropython,SHA2017-badge/micropython-esp32,Peetz0r/micropython-esp32,TDAbboud/micropython,micropython/micropython-esp32,hiway/micropython,oopy/micropython,pozetroninc/micropython,deshipu/micropython,adafruit/circuitpython,SHA2017-badge/micropython-esp32,oopy/micropython,PappaPeppar/micropython,pozetroninc/micropython,henriknelson/micropython,blazewicz/micropython,chrisdearman/micropython,oopy/micropython,infinnovation/micropython,PappaPeppar/micropython,trezor/micropython,infinnovation/micropython,kerneltask/micropython,Timmenem/micropython,lowRISC/micropython,ryannathans/micropython,adafruit/micropython,cwyark/micropython,tobbad/micropython,AriZuu/micropython,adafruit/micropython,dmazzella/micropython,adafruit/circuitpython,MrSurly/micropython,torwag/micropython,Timmenem/micropython,henriknelson/micropython,MrSurly/micropython-esp32,deshipu/micropython,adafruit/circuitpython,Timmenem/micropython,micropython/micropython-esp32,TDAbboud/micropython,pramasoul/micropython,swegener/micropython,puuu/micropython,deshipu/micropython,Timmenem/micropython,HenrikSolver/micropython,HenrikSolver/micropython,pozetroninc/micropython,SHA2017-badge/micropython-esp32,adafruit/circuitpython,TDAbboud/micropython,tralamazza/micropython,trezor/micropython,tobbad/micropython,swegener/micropython,pozetroninc/micropython,pramasoul/micropython,AriZuu/micropython,hiway/micropython,trezor/micropython,deshipu/micropython,chrisdearman/micropython,chrisdearman/micropython,tralamazza/micropython,Peetz0r/micropython-esp32,TDAbboud/micropython,bvernoux/micropython,ryannathans/micropython,MrSurly/micropython-esp32,TDAbboud/micropython,henriknelson/micropython,puuu/micropython,torwag/micropython,oopy/micropython,infinnovation/micropython,tobbad/micropython,blazewicz/micropython,cwyark/micropython,henriknelson/micropython,tobbad/micropython,Peetz0r/micropython-esp32,adafruit/micropython,toolmacher/micropython,SHA2017-badge/micropython-esp32,kerneltask/micropython,trezor/micropython,lowRISC/micropython,lowRISC/micropython,MrSurly/micropython,bvernoux/micropython,MrSurly/micropython-esp32,dmazzella/micropython,micropython/micropython-esp32,pramasoul/micropython,alex-robbins/micropython,PappaPeppar/micropython,ryannathans/micropython,hiway/micropython,pramasoul/micropython,tralamazza/micropython,chrisdearman/micropython,Peetz0r/micropython-esp32,PappaPeppar/micropython,puuu/micropython,selste/micropython,kerneltask/micropython,pfalcon/micropython,pramasoul/micropython,HenrikSolver/micropython,trezor/micropython,AriZuu/micropython,chrisdearman/micropython,pozetroninc/micropython,lowRISC/micropython,tralamazza/micropython,HenrikSolver/micropython,tobbad/micropython,bvernoux/micropython,toolmacher/micropython,alex-robbins/micropython,pfalcon/micropython,selste/micropython,torwag/micropython,hiway/micropython,alex-robbins/micropython,adafruit/circuitpython,pfalcon/micropython,hiway/micropython,selste/micropython,selste/micropython,ryannathans/micropython,cwyark/micropython,AriZuu/micropython,SHA2017-badge/micropython-esp32,deshipu/micropython,pfalcon/micropython,infinnovation/micropython,oopy/micropython,toolmacher/micropython,torwag/micropython,cwyark/micropython,adafruit/micropython,MrSurly/micropython-esp32,MrSurly/micropython-esp32,alex-robbins/micropython,bvernoux/micropython,adafruit/micropython,ryannathans/micropython,puuu/micropython,selste/micropython,Peetz0r/micropython-esp32