legacy: marked BR2_PACKAGE_GCC_TARGET and BR2_HAVE_DEVFILES as removed

These 2 symbols were removed when the gcc has been converted to the
Buildroot package infrastructures.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>