vendor/Rust: more comprehensive dependency removal

[liushuyu]

This pull request simplifies the vendored dependency removal process using a new tool from dh-cargo (currently unreleased).

Additionally, I added one more command to remove the js-sys* stuff (some Rust libraries can be compiled into WebAssembly modules, which will pull in some JavaScript platform libraries for web browser interactions).

[setharnold]

I'm curious about removing js-sys* -- what if that portion is the goal of the package? we do ship web things, eg ckeditor and probably more.

Thanks

[cpaelzer]

This is still Draft, so not reviewing in depth.
But in general while I like that this gets a proper tool, due to it being only available in future should we make it more "use A (old way) or if available the more modern B ( tool)"?