Revert "fieldtrial_testing_config for DiscardCodeCacheAfterFirstUse"

This reverts commit db50a5ab.

Reason for revert:

Regression on a few metrics: http://crbug.com/1116715

Original change's description:
> fieldtrial_testing_config for DiscardCodeCacheAfterFirstUse
> 
> We intend to make a wider rollout/experiment of the feature to discard
> the code cache. No changes are expected in the lab. Update the config to
> confirm no effect on bots.
> 
> Bug: 1045052
> Change-Id: I5c0a6443f9cefac93391d957a1fcefffc72adea3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2356709
> Reviewed-by: Steven Holte <holte@chromium.org>
> Commit-Queue: Egor Pasko <pasko@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#798280}

TBR=pasko@chromium.org,holte@chromium.org

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

Bug: 1045052
Change-Id: Ie0d3d9c45320bd61a6959f467185b72596dc439c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2358833Reviewed-by: Egor Pasko <pasko@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798719}

testing/variations/fieldtrial_testing_config.json

@@ -2347,24 +2347,6 @@
             ]
         }
     ],
-    "DiscardCodeCacheAfterFirstUse": [
-        {
-            "platforms": [
-                "android",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "EnableDiscardCodeCacheAfterFirstUse",
-                    "enable_features": [
-                        "DiscardCodeCacheAfterFirstUse"
-                    ]
-                }
-            ]
-        }
-    ],
     "DnsHttpssvc": [
         {
             "platforms": [