Re-enable WPT for RTCPeerConnection-mandatory-getStats

A recent WebRTC CL makes two more tests pass.
Re-enable WPT for RTCPeerConnection-mandatory-getStats
with updated expectations.

Bug: webrtc:7061
Change-Id: Id2891963e19b0cbfa90db6a35b9a7dcfe853434c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2056466
Commit-Queue: Johannes Kron <kron@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742577}

third_party/blink/web_tests/TestExpectations

@@ -6582,10 +6582,6 @@ crbug.com/1050559 [ Linux ] external/wpt/shape-detection/idlharness.https.any.ht
 crbug.com/1050559 [ Linux ] external/wpt/video-raf/idlharness.window.html [ Pass Failure ]
 crbug.com/1050559 [ Linux ] external/wpt/WebCryptoAPI/derive_bits_keys/hkdf.https.any.worker.html?1-1000 [ Pass Failure ]
 
-# Temporarily disable to unblock WebRTC CL roll making it PASS a test.
-crbug.com/webrtc/7061 external/wpt/webrtc/RTCPeerConnection-mandatory-getStats.https.html [ Pass Failure ]
-crbug.com/webrtc/7061 virtual/webrtc-wpt-plan-b/external/wpt/webrtc/RTCPeerConnection-mandatory-getStats.https.html [ Pass Failure ]
-
 # DevTools roll
 crbug.com/1006759 http/tests/devtools/elements/styles-1/edit-value-url-with-color.js [ Skip ]
 crbug.com/1006759 http/tests/devtools/sources/css-outline-dialog.js [ Skip ]

third_party/blink/web_tests/external/wpt/webrtc/RTCPeerConnection-mandatory-getStats.https-expected.txt

 This is a testharness.js-based test.
-Found 76 tests; 49 PASS, 27 FAIL, 0 TIMEOUT, 0 NOTRUN.
+Found 76 tests; 51 PASS, 25 FAIL, 0 TIMEOUT, 0 NOTRUN.
 PASS getStats succeeds
 PASS RTCRtpStreamStats's ssrc
 PASS RTCRtpStreamStats's kind
@@ -49,8 +49,8 @@ FAIL RTCVideoReceiverStats's partialFramesLost assert_true: Is partialFramesLost
 PASS RTCCodecStats's payloadType
 FAIL RTCCodecStats's codecType assert_true: Is codecType present expected true got false
 PASS RTCCodecStats's clockRate
-FAIL RTCCodecStats's channels assert_true: Is channels present expected true got false
-FAIL RTCCodecStats's sdpFmtpLine assert_true: Is sdpFmtpLine present expected true got false
+PASS RTCCodecStats's channels
+PASS RTCCodecStats's sdpFmtpLine
 PASS RTCTransportStats's bytesSent
 PASS RTCTransportStats's bytesReceived
 FAIL RTCTransportStats's rtcpTransportStatsId assert_true: Is rtcpTransportStatsId present expected true got false