Revert of RTCOutboundRTPStreamStats added. (patchset #3 id:80001 of https://codereview.webrtc.org/2456463002/ )

Reason for revert:
Breaks Chrome FYI.
peerconnection_unittest calls RTCStatsReport::Create without  parameters.

Original issue's description:
> RTCOutboundRTPStreamStats[1] added.
>
> This also adds RTCRTPStreamStats[2] which it derives from. Not all stats
> are supported in this CL, this must be addressed before closing the
> issue.
>
> RTCStatsReport also gets a timestamp and ToString.
>
> [1] https://w3c.github.io/webrtc-stats/#outboundrtpstats-dict*
> [2] https://w3c.github.io/webrtc-stats/#streamstats-dict*
>
> BUG=chromium:627816, chromium:657856, chromium:657854
>
> Committed: https://crrev.com/69e9cb08285f6cbcab547c7a5e6aa668fa6f2d29
> Cr-Commit-Position: refs/heads/master@{#14860}

TBR=hta@webrtc.org,deadbeef@webrtc.org,hbos@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:627816, chromium:657856, chromium:657854

Review-Url: https://codereview.webrtc.org/2465223002
Cr-Commit-Position: refs/heads/master@{#14863}
diff --git a/webrtc/api/stats/rtcstats.h b/webrtc/api/stats/rtcstats.h
index d23e928..0876080 100644
--- a/webrtc/api/stats/rtcstats.h
+++ b/webrtc/api/stats/rtcstats.h
@@ -71,8 +71,8 @@
   bool operator==(const RTCStats& other) const;
   bool operator!=(const RTCStats& other) const;
 
-  // Creates a human readable string representation of the stats object, listing
-  // all of its members (names and values).
+  // Creates a human readable string representation of the report, listing all
+  // of its members (names and values).
   std::string ToString() const;
 
   // Downcasts the stats object to an |RTCStats| subclass |T|. DCHECKs that the