packages/linux-lava: hack further to only overlay for linux-lava specifically

wowie wowzers, this is a terrible hack. All this is needed only because
I couldn't for the life of me find a way to override rust-bindgen from
buildLinux.

Simply including the overlay would require rebuilding a crapton of
things that depend on rust-bindgen, so well, this'll have to do for now.

overlays/default.nix

@@ -2,7 +2,6 @@ builtins.map (path: import path) [
   ./android-studio.nix
   ./ccache.nix
   ./eww.nix
-  ./linux-lava.nix
   ./material-icons.nix
   ./rofi.nix
   ./steam.nix