Docs: Fix mermaid diagram, remove stale sections

Docs: Fix mermaid diagram, remove stale sections

- Fix Bus Controller mermaid diagram by adding explicit subgraph IDs
  (sg_bcc, sg_mr, sg_dr, sg_aaf) to avoid node/title collisions that
  caused: Error: Setting AAF as parent of AAF would create a cycle
- Add Subgraph title / node ID collisions to Mermaid syntax pitfalls
- Remove Build verification and Remaining work sections (progress
  tracking content that no longer belongs in a technical reference)

Issue-ID: CIMAN-33
Change-Id: Ifa4dbe444b89ee4c13f2bd47fdc067facdf39b03
Signed-off-by: Matthew Watkins <mwatkins@linuxfoundation.org>