Use `crossplane/build` submodule

[negz]

Description of your changes

See https://github.com/crossplane/crossplane/issues/1583 for context.

It seems like this passes CI, and uptest works. I think the only notable change is that uptest is now going to run tests using regular Crossplane, not UXP.

If this PR looks good, I'll proceed to update:

• https://github.com/crossplane/upjet-provider-template
• https://github.com/crossplane-contrib/provider-upjet-azure
• https://github.com/crossplane-contrib/provider-upjet-gcp

I don't think I can update every Upjet provider myself, but I'm happy to open PRs to update one or two additional popular Upjet-based providers if you have suggestions.

I have:

• [x] Read and followed Crossplane's contribution process.
• [ ] ~Run make reviewable to ensure this PR is ready for review.~
• [ ] ~Added backport release-x.y labels to auto-backport this PR if necessary.~

How has this code been tested

CI and uptest both work against this PR.

[negz]

/test-examples="examples/iam/v1beta1/role.yaml"

[negz]

/test-examples="examples/iam/v1beta1/role.yaml"