Broke Debian9 things in skolo.

Revert "[infra] Upgrade to Debian 10 for GCE tasks."

This reverts commit b5d39b54a399dddb89e7984612ffb1d7f09fdcd0.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> [infra] Upgrade to Debian 10 for GCE tasks.
> 
> Bug: skia:9438
> Change-Id: I1326f55fa8546d141c43ef4c6fcee6f65ed0e600
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/280901
> Commit-Queue: Weston Tracey <westont@google.com>
> Reviewed-by: Eric Boren <borenet@google.com>

TBR=borenet@google.com,westont@google.com

Change-Id: I866444b0b88ebc335a5cda8ab388b621c1b22c36
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:9438
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/281201
Reviewed-by: Weston Tracey <westont@google.com>
Commit-Queue: Weston Tracey <westont@google.com>
3 files changed