Revert "[Android compile server] Use omitempty for "Error" datastore field."
Revert "[Android compile server] Use omitempty for "Error" datastore field."

This reverts commit 0ba780ddad5fd32b1efb76e183f8a17e1a454cd4.

Reason for revert: Apparently datastore:"-,omitempty" makes it treat - as a key.

Original change's description:
> [Android compile server] Use omitempty for "Error" datastore field.
> 
> This is to keep it backward compatible with old entries that have
> "Error".
> 
> Bug: skia:9487
> Change-Id: I0b44e51f608cd728d250bf0f497542c3541c387e
> Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/245362
> Reviewed-by: Eric Boren <borenet@google.com>
> Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

TBR=borenet@google.com,9fa2e7438b8cb730f96b74865492597170561628@google.com

Change-Id: I7b955d72870882bf8c6aa0e019207369b825f76e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:9487
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/245396
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@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