The softdevice is only verified to be working on nrf52832-based
boards. This feature prevents the softdevice from being build for
other, similar targets (e.g. nrf52840-based boards).
The file always exist so no need to do '-include'.
Replaced using:
sed -i 's|-\(include $(RIOTCPU)/.*/Makefile.features\)|\1|' \
$(git grep -l '$(RIOTCPU)/.*/Makefile.features' boards)