[agentserver] demo: revert pyrightconfig.json — wheel install is enough

I added a demo-local pyrightconfig.json earlier in this session to
work around an IDE squiggle. Root cause was much simpler: the venv
just had an OLD wheel (2.0.0b4) cached from way back. Reinstalling
the new 2.0.0b6 wheel (which has TaskRun.__await__) in the venv
makes everything resolve correctly without any pyright config
changes — the IDE was working fine before; this restores that.

Reinstall command:
  pip uninstall -y azure-ai-agentserver-core azure-ai-agentserver-invocations
  pip install sdk/agentserver/azure-ai-agentserver-core \
              sdk/agentserver/azure-ai-agentserver-invocations

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

Author: RaviPidaparthi