Revert "Enable Video-QualityScaling experiment by default"

This reverts commit 066b5b6ed7069d78e17b8ad6fb8c82546b31acea.

Reason for revert: Regressions on iOS testbots.

Original change's description:
> Enable Video-QualityScaling experiment by default
>
> Bug: webrtc:12401
> Change-Id: Iebf3130e785892bb9fddf1012bc46027a21085a4
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/204000
> Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
> Reviewed-by: Åsa Persson <asapersson@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#33091}

TBR=ilnik@webrtc.org,asapersson@webrtc.org

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

Bug: webrtc:12401
Change-Id: I489b805c7741b63c22c16cfce03347179a3e2602
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/205001
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33123}
diff --git a/modules/video_coding/utility/quality_scaler_unittest.cc b/modules/video_coding/utility/quality_scaler_unittest.cc
index d92cffc..d5b22a8 100644
--- a/modules/video_coding/utility/quality_scaler_unittest.cc
+++ b/modules/video_coding/utility/quality_scaler_unittest.cc
@@ -115,7 +115,8 @@
     FieldTrials,
     QualityScalerTest,
     ::testing::Values(
-        "WebRTC-Video-QualityScaling/Enabled-1,2,3,4,5,6,7,8,0.9,0.99,1/"));
+        "WebRTC-Video-QualityScaling/Enabled-1,2,3,4,5,6,7,8,0.9,0.99,1/",
+        ""));
 
 TEST_P(QualityScalerTest, DownscalesAfterContinuousFramedrop) {
   task_queue_.SendTask([this] { TriggerScale(kScaleDown); }, RTC_FROM_HERE);