wlroots: Fix the build on master

I was testing the build on nixos-unstable but
64d50a00 added another patch. Since this
patch is already in 0.48.0 it can't be applied again (overriding Meson
isn't optimal but we can't build wlroots with 0.46.1).

I've also dropped the "-Dxcb-xkb=enabled" flag since it was removed
(replaced with Xinput).

Thanks @kenogo for noticing this :)