Switch to use the Raspberry Pi OS WiFi firmware

The Raspberry Pi OS WiFi firmware appears to be better maintained and it
fixed an issue on the RPi4.

nerves_defconfig

@@ -40,7 +40,6 @@ BR2_PACKAGE_ESPEAK=y
 BR2_PACKAGE_E2FSPROGS=y
 # BR2_PACKAGE_E2FSPROGS_FSCK is not set
 BR2_PACKAGE_LINUX_FIRMWARE=y
-BR2_PACKAGE_LINUX_FIRMWARE_BRCM_BCM43XXX=y
 BR2_PACKAGE_LINUX_FIRMWARE_RALINK_RT2XX=y
 BR2_PACKAGE_RPI_FIRMWARE=y
 BR2_PACKAGE_RPI_FIRMWARE_CUSTOM_VERSION="1.20200902"
@@ -69,3 +68,4 @@ BR2_NERVES_SYSTEM_NAME="nerves_system_rpi3"
 BR2_NERVES_ADDITIONAL_IMAGE_FILES="${NERVES_DEFCONFIG_DIR}/fwup.conf ${NERVES_DEFCONFIG_DIR}/cmdline.txt ${NERVES_DEFCONFIG_DIR}/config.txt"
 BR2_PACKAGE_NBTTY=y
 BR2_PACKAGE_NERVES_CONFIG=y
+BR2_PACKAGE_RPI_DISTRO_FIRMWARE_NONFREE=y