buildroot

binutils: remove support for version 2.23

Now that we have added support for the lastest binutils version 2.26,
it is time to remove the oldest version we currently support, 2.23, in
order to keep only 3 versions: 2.24, 2.25 and 2.26.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>