remove unused code, mostly imports

[karlseguin]

No description provided.

[krichprollsch]

Did you use a tool to cleanup the code?

[karlseguin]

Did you use a tool to cleanup the code?

https://github.com/DonIsaac/zlint

Could be integrated in the CI, but it reported the same 2 errors hundreds of times, and I don't really agree. I guess it can be configured. It has a beautiful log output, I'd love to use that log output in browser!

The first warning was it wants a comment whenever undefined is used. I guess after #597 I should think that's a good idea, but we use undefined a lot.

The second was to favor implicit type instead of @as:

const node_base = @as(NodeExternal, @ptrCast(node_aligned));

should be

const node_base: NodeExternal = @ptrCast(node_aligned);