So that the default configuration for the dev and coverage variants
includes all options set by MICROPY_CONFIG_ROM_LEVEL_EXTRA_FEATURES.
Note that enabling MICROPY_PY_SYS_STDIO_BUFFER on unix doesn't do anything
because unix doesn't use shared/runtime/sys_stdio_mphal.c.
Signed-off-by: Damien George <damien@micropython.org>