Feature gate more dependencies

[kchibisov]

Wayland backend is self contained and only requires
smithay-client-toolkit to work, thus feature gate the
rest of the deps that are only for X11.

[chrisduerr]

As long as CI is happy, everything should be good.

[aloucks]

This reintroduces an issue where the same dependency is specified multiple times (e.g. parking_lot). This created issues in the past where the dependency was updated in one place, but not in the others. This was fixed in #884.

[kchibisov]

This reintroduces an issue where the same dependency is specified multiple times (e.g. parking_lot). This created issues in the past where the dependency was updated in one place, but not in the others. This was fixed in #884.

It's not an issue if someone can at least look at the code when they are bumping things, if they just blindly merge nothing can be done a tthis point.

[chrisduerr]

Also you say that, but this PR removed the duplicate objc dependency which did actually use different versions. So it basically just doesn't change anything.