Remove WebAssembly code gc field trial testing config

Wasm code GC is enabled by default since https://crrev.com/c/1687535,
thus the field trial is not needed any more.

R=jwd@chromium.org
CC=mstarzinger@chromium.org

Bug: 956480
Change-Id: I911faa1109aa76802a15bd2b7df40b3c3f0dc0cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1780833Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#693616}

testing/variations/fieldtrial_testing_config.json

@@ -6395,26 +6395,6 @@
             ]
         }
     ],
-    "V8WasmCodeGC": [
-        {
-            "platforms": [
-                "android",
-                "android_webview",
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "WebAssemblyCodeGC"
-                    ]
-                }
-            ]
-        }
-    ],
     "VariationsHttpDisabled": [
         {
             "platforms": [