Commit 8a917ad2529ea3df5f47e2be5b4edf362d2d03f6 added the gpio_reset_pin()
call to make sure that pins that were used as ADC inputs could subsequently
be used as digital IO. But calling gpio_reset_pin() will enable the
pull-up on the pin and so pull it high for a brief period. Instead use
rtc_gpio_deinit() which will just reconfigure the pin as a digital IO and
do nothing else.
Fixes issue #7079 (see also #5771).
Signed-off-by: Damien George <damien@micropython.org>