revert clipboard feature on linux to fix static linux binary build

[extrawurst]

this reverts the new dependency on clipboard and x11 in turn so that static linux binaries can be build again.
we need to look into a different solution later.

closes #259

[wezm]

One possibility for X11 would be to shell out to xclip or xsel. This is the approach taken by pass and Neovim.

[extrawurst]

@wezm actually considering this now. I guess there is no way to build against a static version of x11 using musl, right?

[extrawurst]

@wezm also see here: #258 (comment)

[wezm]

I guess there is no way to build against a static version of x11 using musl, right?

It's possible but probably not with the x11-clipboard crate.The x11 crate (as opposed to the x11-dl variant) statically links by default. So, if this was used instead then it would be possible. However, I think the xsel/xclip option is best if you don't want to have a dependency on X11 directly.