Update mpconfigboard.mk remove duplicate of upstream flag

Co-authored-by: Dan Halbert <halbert@halwitz.org>

Author: bradanlane

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

@@ -29,7 +29,6 @@ LONGINT_IMPL = NONE
 CIRCUITPY_FULL_BUILD = 0
 
 CIRCUITPY_AUDIOIO = 1
-CIRCUITPY_BITMAPFILTER = 0
 CIRCUITPY_DISPLAYIO = 0
 CIRCUITPY_FRAMEBUFFERIO = 0
 CIRCUITPY_ONEWIREIO = 0