[clang-tidy] Apply modernize-use-override fixes.

This CL applies clang-tidy's modernize-use-override [1] to the
WebRTC codebase.

All changes in this CL are automatically generated by both clang-tidy
and 'git cl format'.

[1] - https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-override.html

Bug: webrtc:10252
Change-Id: I2bb8bd90fa8adb90aa33861fe7c788132a819a20
Reviewed-on: https://webrtc-review.googlesource.com/c/120412
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26461}

modules/remote_bitrate_estimator/bwe_simulations.cc

@@ -36,7 +36,7 @@ class BweSimulation : public BweTest,
  public:
   BweSimulation()
       : BweTest(), random_(Clock::GetRealTimeClock()->TimeInMicroseconds()) {}
-  virtual ~BweSimulation() {}
+  ~BweSimulation() override {}
 
  protected:
   void SetUp() override {