Remove dependency vendoring

[kmoe]

Go language tooling has moved beyond the need for dependency vendoring, so we no longer recommend its use in providers.

This PR does the following:

• delete vendor/ directory
• remove references to this directory in Makefile and build scripts

Once this PR is merged, we will:

• request that any PR modifying the vendor/ directory be rebased onto the main branch in order to prevent this directory being reintroduced
• update internal build tooling to remove use of -mod=vendor from release builds.

[bflad]

Looks good to me 🚀

[github-actions]

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