Revert "Download later: Enable the feature in field trial config."

This reverts commit b6c9ce8c.

Reason for revert: Break tests.

Original change's description:
> Download later: Enable the feature in field trial config.
>
> This CL adds download later feature to fild trial json config file.
>
> TBR=mpearson@chromium.org
>
> Bug: NONE
> Change-Id: I0de7dcb2afeb796ac02083a65a8cf6ee2f205d97
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438576
> Commit-Queue: Xing Liu <xingliu@chromium.org>
> Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#812140}

TBR=mpearson@chromium.org,dtrainor@chromium.org,qinmin@chromium.org,shaktisahu@chromium.org,xingliu@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: NONE
Change-Id: Ia42eb881149a35a274b3e97f16d9adc5884e811c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2446193Reviewed-by: Xing Liu <xingliu@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813296}

testing/variations/fieldtrial_testing_config.json

@@ -2518,7 +2518,6 @@
                 {
                     "name": "Enabled",
                     "enable_features": [
-                        "DownloadLater",
                         "DownloadsAutoResumptionNative"
                     ]
                 }