Clean up javadoc on `Metadata.Entry.populateMediaMetadata`

Remove self-links, and remove section that is documenting internal
ordering behaviour of
[`SimpleBasePlayer.getCombinedMediaMetadata`](https://github.com/google/ExoPlayer/blob/bb270c62cf2f7a1570fe22f87bb348a2d5e94dcf/library/common/src/main/java/com/google/android/exoplayer2/SimpleBasePlayer.java#L1770)
rather than anything specifically about this method.

#minor-release

PiperOrigin-RevId: 490923719
(cherry picked from commit ed8c196e)

library/common/src/main/java/com/google/android/exoplayer2/metadata/Metadata.java

@@ -52,11 +52,8 @@ public final class Metadata implements Parcelable {
     }
 
     /**
-     * Updates the {@link MediaMetadata.Builder} with the type specific values stored in this Entry.
-     *
-     * <p>The order of the {@link Entry} objects in the {@link Metadata} matters. If two {@link
-     * Entry} entries attempt to populate the same {@link MediaMetadata} field, then the last one in
-     * the list is used.
+     * Updates the {@link MediaMetadata.Builder} with the type-specific values stored in this {@code
+     * Entry}.
      *
      * @param builder The builder to be updated.
      */