Remove more redundant TestExpectations

According to webkit_lint, "virtual/*/"-prefixed test expectations are
implied by the non-prefixed ones, so no need to list both of them.
This CL removes two such cases (for
external/wpt/webrtc/RTCPeerConnection-getStats.https.html).

TBR=hta@chromium.org

No-Try: true
Bug: 1092835
Change-Id: Ia5e841194e3ca673245fd6956369d23c67b4774f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2235848Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Auto-Submit: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#776513}

third_party/blink/web_tests/TestExpectations

@@ -6746,9 +6746,7 @@ crbug.com/1091948 [ Linux ] external/wpt/html/canvas/element/manual/fill-and-str
 crbug.com/1092091 [ Mac ] virtual/dark-color-scheme/datetimelocal-picker/datetimelocal-open.html [ Pass Failure ]
 
 # Test giving differing results on different build bots
-crbug.com/1092721 [ Mac ] virtual/webrtc-wpt-plan-b/external/wpt/webrtc/RTCPeerConnection-getStats.https.html [ Pass Failure ]
 crbug.com/1092721 [ Mac ] external/wpt/webrtc/RTCPeerConnection-getStats.https.html [ Pass Failure ]
-crbug.com/1092721 [ Linux ] virtual/webrtc-wpt-plan-b/external/wpt/webrtc/RTCPeerConnection-getStats.https.html [ Pass Failure ]
 crbug.com/1092721 [ Linux ] external/wpt/webrtc/RTCPeerConnection-getStats.https.html [ Pass Failure ]
 
 # Sheriff 2020-06-06