Misc cleanup

Group up some other minor changes with the vorbis comment utils.

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/VorbisUtil.java

@@ -331,7 +331,7 @@ public final class VorbisUtil {
    * @param scratch The bytes of the picture.
    * @return A picture frame from the scratch data.
    */
-  public static PictureFrame buildPictureFrame(ParsableByteArray scratch) {
+  /* package */ static PictureFrame buildPictureFrame(ParsableByteArray scratch) {
     int pictureType = scratch.readInt();
     int mimeTypeLength = scratch.readInt();
     String mimeType = scratch.readString(mimeTypeLength, Charsets.US_ASCII);

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/ogg/OpusReader.java

@@ -87,7 +87,6 @@ import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
       checkNotNull(setupData.format); // Has been set when the header was read
 
       int startPosition = packet.getPosition();
-
       if (!validateCommentHeaderSignature(packet)) {
         packet.setPosition(startPosition);
         return false;

library/extractor/src/main/java/com/google/android/exoplayer2/metadata/vorbis/PictureFrame.java

@@ -24,7 +24,7 @@ import com.google.android.exoplayer2.MediaMetadata;
 import com.google.android.exoplayer2.metadata.Metadata;
 import java.util.Arrays;
 
-/** A picture parsed from a FLAC file. */
+/** A picture parsed from a Vorbis Comment or a FLAC metadata block. */
 public class PictureFrame implements Metadata.Entry {
 
   /** The type of the picture. */