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/decoding_state.cc b/modules/video_coding/decoding_state.cc
index 1d54063..23bf668 100644
--- a/modules/video_coding/decoding_state.cc
+++ b/modules/video_coding/decoding_state.cc
@@ -58,7 +58,7 @@
   assert(frame != NULL);
   if (in_initial_state_)
     return false;
-  return !IsNewerTimestamp(frame->Timestamp(), time_stamp_);
+  return !IsNewerTimestamp(frame->TimeStamp(), time_stamp_);
 }
 
 bool VCMDecodingState::IsOldPacket(const VCMPacket* packet) const {
@@ -73,7 +73,7 @@
   if (!UsingFlexibleMode(frame))
     UpdateSyncState(frame);
   sequence_num_ = static_cast<uint16_t>(frame->GetHighSeqNum());
-  time_stamp_ = frame->Timestamp();
+  time_stamp_ = frame->TimeStamp();
   picture_id_ = frame->PictureId();
   temporal_id_ = frame->TemporalId();
   tl0_pic_id_ = frame->Tl0PicId();
@@ -143,7 +143,7 @@
     // Continuous empty packets or continuous frames can be dropped if we
     // advance the sequence number.
     sequence_num_ = frame->GetHighSeqNum();
-    time_stamp_ = frame->Timestamp();
+    time_stamp_ = frame->TimeStamp();
     return true;
   }
   return false;