Revert "Dockerfile: switch to "skia" user at end"
Revert "Dockerfile: switch to "skia" user at end"

This reverts commit 68ddf6cc74d78b066b85f4f61f65bb38767a3b0a.

Reason for revert: didn't help

Original change's description:
> Dockerfile: switch to "skia" user at end
> 
> Change-Id: Ie5558e0fd84fcba0aec9c5f6cfd83eeea089bf31
> Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/212220
> Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
> Auto-Submit: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
> Reviewed-by: Kevin Lubick <kjlubick@google.com>

TBR=0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com,kjlubick@google.com

Change-Id: I3dcb7b78e8e68cdcd7d6ff145af145ac16bf42ea
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/212420
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot