* Fix tick labels for background FN/FP

In the confusion matrix.

* Remove FP/FN from the background labels of the confusion matrix

* Update metrics.py
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>