Remove and correct outdated docs relating to include/ and include/global_project.

[jordivandooren]

Resolves #10725

Problem

Several docs reference parts of include/ that have been removed from dbt-core.

Solution

Remove references to the global_project in the docs and correct the responsibility of the include/ folder in the ARCHITECTURE.md document.

Checklist

• I have read the contributing guide and understand what's expected of me.
• I have run this code in development, and it appears to resolve the stated issue.
• This PR includes tests, or tests are not required or relevant for this PR.
• This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• This PR includes type annotations for new and modified functions.