Fix docs on MediaItem.Builder#setDrmUuid

The docs on setLicenseUri say it's optional, and it has been since
https://github.com/google/ExoPlayer/commit/379cd8a04f0bf44a9422a08440223581b2657d74
(which should have changed this javadoc too)

#minor-release

PiperOrigin-RevId: 376139158

library/common/src/main/java/com/google/android/exoplayer2/MediaItem.java

@@ -284,8 +284,7 @@ public final class MediaItem implements Bundleable {
     }
 
     /**
-     * Sets the {@link UUID} of the protection scheme. If a DRM system UUID is set, the {@link
-     * DrmConfiguration#licenseUri} needs to be set as well.
+     * Sets the {@link UUID} of the protection scheme.
      *
      * <p>If {@link #setUri} is passed a non-null {@code uri}, the DRM system UUID is used to create
      * a {@link PlaybackProperties} object. Otherwise it will be ignored.