Delete a gcc workaround in rtc::FinalRefCountedObject

with bot using old version of gcc removed, this workaround is not needed.

Bug: webrtc:12481
Change-Id: Ib1bfb6260c7ff5688c39fa05e8a62225700b9f27
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213187
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33592}
diff --git a/rtc_base/ref_counted_object.h b/rtc_base/ref_counted_object.h
index e86a1fb..873eacc 100644
--- a/rtc_base/ref_counted_object.h
+++ b/rtc_base/ref_counted_object.h
@@ -80,14 +80,7 @@
  private:
   ~FinalRefCountedObject() = default;
 
-  // gcc v7.1 requires default contructors for members of
-  // `FinalRefCountedObject` to be able to use inherited constructors.
-  // TODO(danilchap): Replace with simpler braced initialization when
-  // bot support for that version of gcc is dropped.
-  class ZeroBasedRefCounter : public webrtc::webrtc_impl::RefCounter {
-   public:
-    ZeroBasedRefCounter() : RefCounter(0) {}
-  } mutable ref_count_;
+  mutable webrtc::webrtc_impl::RefCounter ref_count_{0};
 };
 
 }  // namespace rtc