Fix up GHE_NUM_SNAPSHOTS presence and number format test
Fix up GHE_NUM_SNAPSHOTS presence and number format test

I removed the explicit checks in ghe-prune-snapshots since the
script will fail naturally when GHE_NUM_SNAPSHOTS is set to a
non-numeric value. The not set cases uses the new default of 10
snapshots instead of failing.

github/backup-utils,github/backup-utils,spotify/backup-utils,Teino1978-Corp/https-github.com-Teino1978-Corp-backup-utils