ext: Remove dead code from configuration.py

ext: Remove dead code from configuration.py

This has been tested with vulture:
https://pypi.org/project/vulture

JIRA: https://gem5.atlassian.net/projects/GEM5/issues/GEM5-533

Change-Id: Ibaf812ace94c2ae0e2115552a87fb506a427bb89
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30242
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>