py/objstr: Convert some instances of mp_uint_t to size_t.
py/objstr: Convert some instances of mp_uint_t to size_t.

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