Revert "Add Timestamp accessor methods to the EncodedImage class."

This reverts commit f34d467b03da4f20a1d036a20966fcad43d2433f.

Reason for revert: Seems to break downstream project.

Original change's description:
> Add Timestamp accessor methods to the EncodedImage class.
> 
> Bug: webrtc:9378
> Change-Id: I59bf14f631f92f0f4e05f60d4af25641a23a53f9
> Reviewed-on: https://webrtc-review.googlesource.com/82100
> Reviewed-by: Stefan Holmer <stefan@webrtc.org>
> Reviewed-by: Philip Eliasson <philipel@webrtc.org>
> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#23734}

TBR=brandtr@webrtc.org,nisse@webrtc.org,stefan@webrtc.org,philipel@webrtc.org

Change-Id: I3aa0c0119426886bc583c918aae862eb7f4b6b63
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9378
Reviewed-on: https://webrtc-review.googlesource.com/85600
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23739}
diff --git a/modules/video_coding/receiver.cc b/modules/video_coding/receiver.cc
index 4ed61da..a1eeded 100644
--- a/modules/video_coding/receiver.cc
+++ b/modules/video_coding/receiver.cc
@@ -140,7 +140,7 @@
       jitter_buffer_.NextCompleteFrame(max_wait_time_ms);
 
   if (found_frame) {
-    frame_timestamp = found_frame->Timestamp();
+    frame_timestamp = found_frame->TimeStamp();
     min_playout_delay_ms = found_frame->EncodedImage().playout_delay_.min_ms;
     max_playout_delay_ms = found_frame->EncodedImage().playout_delay_.max_ms;
   } else {
@@ -212,7 +212,7 @@
     return NULL;
   }
   frame->SetRenderTime(render_time_ms);
-  TRACE_EVENT_ASYNC_STEP1("webrtc", "Video", frame->Timestamp(), "SetRenderTS",
+  TRACE_EVENT_ASYNC_STEP1("webrtc", "Video", frame->TimeStamp(), "SetRenderTS",
                           "render_time", frame->RenderTimeMs());
   if (!frame->Complete()) {
     // Update stats for incomplete frames.