Remove unused plot_congestion.py and plot_floorplan.py

Some ad hoc testing scripts

These utility scripts are not referenced anywhere in the codebase.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe