local.conf.sample: do not add sdl to nativesdk qemu config

This is unnecessary as the recipe itself already does it:
http://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/meta/recipes-devtools/qemu/qemu_4.0.0.bb?id=1a4e4fb6b0a9d54641bd4193e95311d1f822a9ca#n21



(From meta-yocto rev: ada58683641b8a15e8b2e44060437a9c67d532e1)

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>