Revert of "Create rtc::AtomicInt POD struct." (patchset #3 id:40001 of https://codereview.webrtc.org/1498953002/ )

Reason for revert:
Broke downstream compile step, possibly relandable when using a MSVC version that has constexpr, other than that I'm out of ideas.

.../webrtc/base/atomicops.h:71:8: note:   no known conversion for argument 1 from '<brace-enclosed initializer list>' to 'const rtc::AtomicInt&'

Original issue's description:
> Reland of "Create rtc::AtomicInt POD struct."
>
> Relands https://codereview.webrtc.org/1420043008/ with brace initializers
> instead of constructors hoping that they won't introduce static
> initializers.
>
> BUG=
> R=tommi@webrtc.org
>
> Committed: https://crrev.com/84f0970d100e67a1dc4fe9a1b16b7d293302044e
> Cr-Commit-Position: refs/heads/master@{#10920}

TBR=tommi@webrtc.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.webrtc.org/1505053002

Cr-Commit-Position: refs/heads/master@{#10922}
diff --git a/webrtc/system_wrappers/source/trace_impl.cc b/webrtc/system_wrappers/source/trace_impl.cc
index 3bf1f1b..5029f5a 100644
--- a/webrtc/system_wrappers/source/trace_impl.cc
+++ b/webrtc/system_wrappers/source/trace_impl.cc
@@ -34,7 +34,7 @@
 const int Trace::kBoilerplateLength = 71;
 const int Trace::kTimestampPosition = 13;
 const int Trace::kTimestampLength = 12;
-rtc::AtomicInt Trace::level_filter_ = {kTraceDefault};
+volatile int Trace::level_filter_ = kTraceDefault;
 
 // Construct On First Use idiom. Avoids "static initialization order fiasco".
 TraceImpl* TraceImpl::StaticInstance(CountOperation count_operation,
@@ -548,12 +548,12 @@
 
 // static
 void Trace::set_level_filter(int filter) {
-  rtc::AtomicInt::ReleaseStore(&level_filter_, filter);
+  rtc::AtomicOps::ReleaseStore(&level_filter_, filter);
 }
 
 // static
 int Trace::level_filter() {
-  return rtc::AtomicInt::AcquireLoad(&level_filter_);
+  return rtc::AtomicOps::AcquireLoad(&level_filter_);
 }
 
 // static