Update mpconfigboard.mk remove duplicate of upstream flag

Co-authored-by: Dan Halbert <[email protected]>

Author: bradanlane

ports/atmel-samd/boards/bradanlanestudio_coin_m0/mpconfigboard.mk

@@ -32,7 +32,6 @@ CIRCUITPY_AUDIOIO = 1
 CIRCUITPY_BITMAPFILTER = 0
 CIRCUITPY_DISPLAYIO = 0
 CIRCUITPY_FRAMEBUFFERIO = 0
-CIRCUITPY_MAX3421E = 0
 CIRCUITPY_ONEWIREIO = 0
 CIRCUITPY_PULSEIO = 0
 CIRCUITPY_RGBMATRIX = 0