Update mpconfigboard.mk remove encapulated build flag

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

Author: bradanlane

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

@@ -37,7 +37,6 @@ CIRCUITPY_ONEWIREIO = 0
 CIRCUITPY_PULSEIO = 0
 CIRCUITPY_RGBMATRIX = 0
 CIRCUITPY_ROTARYIO = 0
-CIRCUITPY_ROTARYIO_SOFTENCODER = 0
 CIRCUITPY_RTC = 0
 CIRCUITPY_USB_HID = 1
 CIRCUITPY_USB_MIDI = 0