removeEmeSessions() {
    return this.startOperation_(this.removeEmeSessions_());
  }
Removes any orphaned EME sessions.

When DRM content is stored offline with a persistent session, the DRM
session ID is stored in the offline content database. When DRM content
gets deleted from the database, EME is asked to release the underlying
session attached to that ID.

If for some reason that fails, or if the browser is closed before that
asynchronous process is completed, session IDs must still be tracked in
the database. Otherwise, they would get orphaned and there would be no way
to discover them or clean them up.

This method will clean up any orphaned, persistent DRM sessions that the
database is still tracking. It should be called on application startup,
and will do nothing if there are no orphaned DRM sessions. It returns a
Promise that resolves to true if all the sessions were successfully
removed, or false if there are still sessions remaining.

@return {!Promise<boolean>}
@export