Delete VCMEncodedFrame methods Buffer and MutableBuffer

Replaced by inherited method EncodedImage::data().

Bug: webrtc:9378
Change-Id: I4ec75148f578c72ffb407f9cbf6b4232cc9cfcf6
Reviewed-on: https://webrtc-review.googlesource.com/c/116962
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26212}
diff --git a/modules/video_coding/jitter_buffer_unittest.cc b/modules/video_coding/jitter_buffer_unittest.cc
index e95a312..c2f5ed3 100644
--- a/modules/video_coding/jitter_buffer_unittest.cc
+++ b/modules/video_coding/jitter_buffer_unittest.cc
@@ -272,7 +272,7 @@
                      bool startCode) {
     ASSERT_TRUE(frame_out);
 
-    const uint8_t* outData = frame_out->Buffer();
+    const uint8_t* outData = frame_out->data();
     unsigned int i = 0;
 
     if (startCode) {