Remove i386 support from binary-release-based 10 variants

[tianon]

This copies the current architectures file into 8/ and then removes i386 from all but Alpine (where it's built from source).

The justification here is that https://nodejs.org/dist/v10.6.0/node-v10.6.0-linux-x86.tar.xz is a 404 (appears 32bit builds are no longer generated).

[chorrell]

Do we know if the x86 build was dropped on purpose or is this an error with the build and release process?

[nschonni]

See nodejs/build#885

[tianon]

That thread makes it seem like it's still under discussion, but the builds are definitely gone (as noted in nodejs/node#20327). 😕

[chorrell]

Let merge this and then redo the v11 release to use stretch for slim and the main variant