cluster: cleanup unused scripts

Verified with k/k and k/test-infra.

- restore-from-backup.sh
Performs restoration of etcd snapshots and the logic seems valid
on a quick look, but doesn't seem to be used anywhere in our infra.
I suspect this is used on demand for local testing, but /cluster root
doesn't seem like the right place for it at this point.
- test-*.sh
Gikgo related calls but these bash scripts seem unused in the infra.

Author: neolit123