RFR (JDK 12): 6899533: SecureClassLoader and URLClassLoader have unnecessary check for createClassLoader permission

[Sean Mullan]

Please review this change to remove code that is no longer necessary now 
that pre-JDK 1.2 SecurityManager methods are no longer supported [1]. In 
addition, the initialized flag and associated code has been removed from 
SecureClassLoader as this was only necessary to prevent finalizer 
attacks prior to JDK 6.

webrev: http://cr.openjdk.java.net/~mullan/webrevs/6899533/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-6899533

--Sean

[1] https://bugs.openjdk.java.net/browse/JDK-8189750