It should be safe to remove this code now, as it was probably used to safeguard against malicious subclasses, see https://www.oracle.com/technetwork/java/seccodeguide-139067.html#4-5 for more info. These issues were fixed in JDK 6.

However, it is worth a closer look to make sure before removing.

See also the discussion thread at http://mail.openjdk.java.net/pipermail/security-dev/2018-December/019002.html.