chore(Squad.Agents.AI): remove outdated draft PR body file

The standalone pr-body.md was an early draft authored before the live PR description took its final shape. The PR body on GitHub is the canonical source; this file is dead weight and would confuse maintainers reviewing the diff.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: tamirdresher