py/runtime: Unlock the GIL in mp_deinit function.
py/runtime: Unlock the GIL in mp_deinit function.

This mirrors what is done in mp_init.  Some RTOSs require this symmetry to
get back to a clean state (when doing a soft reset, for example).

tobbad/micropython,pozetroninc/micropython,MrSurly/micropython,selste/micropython,kerneltask/micropython,selste/micropython,pramasoul/micropython,MrSurly/micropython,adafruit/circuitpython,MrSurly/micropython,henriknelson/micropython,adafruit/circuitpython,henriknelson/micropython,pozetroninc/micropython,pfalcon/micropython,pfalcon/micropython,selste/micropython,bvernoux/micropython,kerneltask/micropython,MrSurly/micropython,adafruit/circuitpython,adafruit/circuitpython,trezor/micropython,henriknelson/micropython,kerneltask/micropython,bvernoux/micropython,bvernoux/micropython,bvernoux/micropython,pramasoul/micropython,trezor/micropython,trezor/micropython,tobbad/micropython,henriknelson/micropython,tobbad/micropython,trezor/micropython,bvernoux/micropython,tobbad/micropython,kerneltask/micropython,adafruit/circuitpython,pfalcon/micropython,pfalcon/micropython,kerneltask/micropython,MrSurly/micropython,selste/micropython,adafruit/circuitpython,pramasoul/micropython,pramasoul/micropython,pramasoul/micropython,trezor/micropython,pozetroninc/micropython,henriknelson/micropython,selste/micropython,tobbad/micropython,pozetroninc/micropython,pfalcon/micropython,pozetroninc/micropython