lib/libm/math: Remove implementations of float conversion functions.
lib/libm/math: Remove implementations of float conversion functions.

These implementations are incorrect (eg f2d and d2f don't handle special
values like 0.0) and proper versions can be provided by libgcc (or
equivalent depending on the toolchain).

libgcc is now linked with the stmhal port so that library will provide
these functions from now on.

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