Revert "[GetStats] Expose video codec implementation in standardized metrics."

This reverts commit 2b9fa09fa3e3379fd8e76490c394f25670352ef2.

Reason for revert: speculative revert since it seems to break Chrome FYI bots. See https://ci.chromium.org/p/chromium/builders/webrtc.fyi/WebRTC%20Chromium%20FYI%20Linux%20Tester/4206

Original change's description:
> [GetStats] Expose video codec implementation in standardized metrics.
> 
> Spec issue: https://github.com/w3c/webrtc-stats/issues/445
> Spec PR: https://github.com/w3c/webrtc-stats/pull/473
> 
> Now that the spec's RTCCodecStats.implementation has moved to
> RTCOutboundRtpStreamStats.encoderImplementation and
> RTCInboundRtpStreamStats.decoderImplementation, this CL implements them
> using the same string that the legacy getStats() API used.
> 
> Bug: webrtc:10890
> Change-Id: Ic43ce44735453626791959df3061ee253356015a
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/149168
> Commit-Queue: Henrik Boström <hbos@webrtc.org>
> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#28877}

TBR=ilnik@webrtc.org,hbos@webrtc.org

Change-Id: Ia0b7f9806564cf28881c50d6371b8141a22e3431
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:10890
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/149175
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Commit-Queue: Henrik Andreassson <henrika@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28879}
diff --git a/api/stats/rtcstats_objects.h b/api/stats/rtcstats_objects.h
index b492203..8955c4e 100644
--- a/api/stats/rtcstats_objects.h
+++ b/api/stats/rtcstats_objects.h
@@ -122,6 +122,8 @@
   RTCStatsMember<uint32_t> channels;
   // TODO(hbos): Collect and populate this value. https://bugs.webrtc.org/7061
   RTCStatsMember<std::string> sdp_fmtp_line;
+  // TODO(hbos): Collect and populate this value. https://bugs.webrtc.org/7061
+  RTCStatsMember<std::string> implementation;
 };
 
 // https://w3c.github.io/webrtc-stats/#dcstats-dict*
@@ -445,9 +447,6 @@
   RTCStatsMember<double> total_decode_time;
   // https://henbos.github.io/webrtc-provisional-stats/#dom-rtcinboundrtpstreamstats-contenttype
   RTCStatsMember<std::string> content_type;
-  // TODO(hbos): This is only implemented for video; implement it for audio as
-  // well.
-  RTCStatsMember<std::string> decoder_implementation;
 };
 
 // https://w3c.github.io/webrtc-stats/#outboundrtpstats-dict*
@@ -483,9 +482,6 @@
   RTCStatsMember<std::string> quality_limitation_reason;
   // https://henbos.github.io/webrtc-provisional-stats/#dom-rtcoutboundrtpstreamstats-contenttype
   RTCStatsMember<std::string> content_type;
-  // TODO(hbos): This is only implemented for video; implement it for audio as
-  // well.
-  RTCStatsMember<std::string> encoder_implementation;
 };
 
 // TODO(https://crbug.com/webrtc/10671): Refactor the stats dictionaries to have