Remove -pt image use

[dougbu]

• This issue is blocking
• This issue is causing unreasonable pain

The -pt images in our pools are redundant and add nothing except extra verbiage for our customers. Unfortunately they're referenced in some dotnet/arcade branches. Need to check all of the branches below and remove that usage if found.

• release/6.0
• release/7.0 — if branch lasts long enough
• release/8.0
• main

[riarenas]

PRs to all branches have been merged.

[dougbu]

Not quite done. @chcosta opened #14717 because #14694 reverted 'main' to its previous -pt image use. Reopening and co-assigning to @chcosta (for final closure after PR is merged and arcade-validation is done)…