Revert "Enable and fix chromium clang warnings in rtp_rtcp test targets"

This reverts commit 9486b117daac09c9f7ac8450ccda835938cf3150.

Reason for revert: Breaks downstream project

Original change's description:
> Enable and fix chromium clang warnings in rtp_rtcp test targets
> 
> Bug: webrtc:163
> Change-Id: I4ed3e63296d8bf06536a83196d597c7a906ba11c
> Reviewed-on: https://webrtc-review.googlesource.com/60802
> Reviewed-by: Björn Terelius <terelius@webrtc.org>
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#22357}

TBR=danilchap@webrtc.org,phoglund@webrtc.org,terelius@webrtc.org

Change-Id: I2c3777ea9f26813bdb395e7fd68f6b49443586ea
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:163
Reviewed-on: https://webrtc-review.googlesource.com/61060
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22365}

modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc

@@ -42,7 +42,7 @@ const int64_t kMaxRttMs = 1000;
 class RtcpRttStatsTestImpl : public RtcpRttStats {
  public:
   RtcpRttStatsTestImpl() : rtt_ms_(0) {}
-  ~RtcpRttStatsTestImpl() override = default;
+  virtual ~RtcpRttStatsTestImpl() {}
 
   void OnRttUpdate(int64_t rtt_ms) override { rtt_ms_ = rtt_ms; }
   int64_t LastProcessedRtt() const override { return rtt_ms_; }