Removes unrelated references to diagrams.

Disk labels were referred to diagrams which was not requried at this
stage of learning for the students. This patch removes the references to the
diagrams to avoid confusion.

Change-Id: I3fc41cf7a96916b2f3eadfba953fa5f9e26c095a
Closes-Bug: #1267673
Implements: blueprint training-manuals
Merge "Removes unrelated references to diagrams."