Use backticks not vertical bars to denote variables in comments for /sdk

Bug: webrtc:12338
Change-Id: Ifaad29ccb63b0f2f3aeefb77dae061ebc7f87e6c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227024
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34561}

sdk/android/api/org/webrtc/VideoEncoder.java

@@ -238,7 +238,7 @@ public interface VideoEncoder {
 
   public interface Callback {
     /**
-     * Old encoders assume that the byte buffer held by |frame| is not accessed after the call to
+     * Old encoders assume that the byte buffer held by `frame` is not accessed after the call to
      * this method returns. If the pipeline downstream needs to hold on to the buffer, it then has
      * to make its own copy. We want to move to a model where no copying is needed, and instead use
      * retain()/release() to signal to the encoder when it is safe to reuse the buffer.