Remove UseTextForUpdateButton from testing config

This experiment is default-enabled and being launched to 100% stable.

Bug: 1002162
Change-Id: I1b0927ceb51d41fd298d94f4e0e2fdcd31205168
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2520813
Auto-Submit: Peter Boström <pbos@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824609}

testing/variations/fieldtrial_testing_config.json

@@ -7182,24 +7182,6 @@
             ]
         }
     ],
-    "UseTextForUpdateButton": [
-        {
-            "platforms": [
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "UseTextForUpdateButton",
-                    "enable_features": [
-                        "UseTextForUpdateButton"
-                    ]
-                }
-            ]
-        }
-    ],
     "UserAgentClientHintRollout": [
         {
             "platforms": [