default.xml: removing device specific repos as breakfast is now supported by us

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
default.xml: removing not used prebuilt toolchain repos (empty + darwin)

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
Signed-off-by: Sergio Schvezov <sergio.schvezov@canonical.com>
default.xml: removing old aosp based prebuilt repo (we're using the ones from prebuilts)

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
Signed-off-by: Sergio Schvezov <sergio.schvezov@canonical.com>
default.xml: removing not used pre-built toolchain files (old androideabi, mipsel and i686)

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
Signed-off-by: Sergio Schvezov <sergio.schvezov@canonical.com>