Revert "Reland "Activating AVX2 support by default""

This reverts commit a0ad0bbf8f4b7a20c6efb6950ede2a44205b2b74.

Reason for revert: Speculative revert. I suspect it breaks downstream project

Original change's description:
> Reland "Activating AVX2 support by default"
>
> This is a reland of ad148272b89394978915cb00e1c1be552d908a42
>
> Original change's description:
> > Activating AVX2 support by default
> >
> > This CL activates the newly added AVX2 support by default.
> > The activation is done beneath a kill-switch.
> >
> > Beyond the above, the CL also changes an incorrect DCHECK_GT
> > to a DCHECK_GE.
> >
> > Bug: webrtc:11663
> > Change-Id: I231ccb2f5efabf74cd8190411daa954b2b94a2a0
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/183042
> > Commit-Queue: Per Åhgren <peah@webrtc.org>
> > Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> > Reviewed-by: Sam Zackrisson <saza@webrtc.org>
> > Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#32193}
>
> Bug: webrtc:11663
> Change-Id: Ib41dc1d1c5865f2828699c462939d15d5562df47
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/186262
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Reviewed-by: Sam Zackrisson <saza@webrtc.org>
> Commit-Queue: Per Åhgren <peah@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#32270}

TBR=mbonadei@webrtc.org,saza@webrtc.org,peah@webrtc.org,kwiberg@webrtc.org

Change-Id: I1305fad8d19ba0bd69a38b9e2959af54f900535d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:11663
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/186304
Reviewed-by: Andrey Logvin <landrey@webrtc.org>
Commit-Queue: Andrey Logvin <landrey@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32273}
diff --git a/system_wrappers/source/cpu_features.cc b/system_wrappers/source/cpu_features.cc
index 0f81212..e40c65a 100644
--- a/system_wrappers/source/cpu_features.cc
+++ b/system_wrappers/source/cpu_features.cc
@@ -12,7 +12,6 @@
 
 #include "rtc_base/system/arch.h"
 #include "system_wrappers/include/cpu_features_wrapper.h"
-#include "system_wrappers/include/field_trial.h"
 
 #if defined(WEBRTC_ARCH_X86_FAMILY) && defined(_MSC_VER)
 #include <intrin.h>
@@ -78,8 +77,7 @@
     return 0 != (cpu_info[2] & 0x00000001);
   }
 #if defined(WEBRTC_ENABLE_AVX2)
-  if (feature == kAVX2 &&
-      !webrtc::field_trial::IsEnabled("WebRTC-Avx2SupportKillSwitch")) {
+  if (feature == kAVX2) {
     int cpu_info7[4];
     __cpuid(cpu_info7, 0);
     int num_ids = cpu_info7[0];