x/tools/godoc/vfs/zipfs: remove zipfs package

[broady]

Once golang.org/cl/133355 is in, and #27205 is resolved, I don't think we need the zipfs package for godoc anymore.

As far as I know, it was created as a workaround for Google App Engine restrictions on number of files allowed in an app deployment.

[dmitshur]

Such a change would affect its users.

Do we have a policy to follow to removing non-internal subrepo packages? How do we decide when to do it? How to do it (perhaps deprecate first, remove after some pre-determined time; or something else)?

[SamWhited]

Can we move this to the subrepos? I use this package heavily in several products.

EDIT: higher-up in the subrepos, outside of the godoc tree, that is.

[seankhliao]

I believe removal won't happend for x/ repos.

[dmitshur]

By now we have answers to that question from 6 years ago about how to do this: removing a golang.org/x package involves deprecating it, isolating it to its own nested module, tagging that, and then deleting from main branch. See past examples like #57051, #56783, #59676, #70229, and so on (also see #60557 which is about documenting the process better).

This issue would need to go through the proposal process, though.