ProxyFactory leaks classloader if SFSB is used

org.jboss.ejb.ProxyFactory holds a ref to the constructor used to instantiate SFSBs after it is destroyed. This leaks the the application's classloader to the Container instance's proxyFactoryTL ThreadLocal.

Immediate solution is to clear the constructor ref in ProxyFactory.destroy(). Later we need to see why ProxyFactoryFinderInterceptor isn't making the call that clears the ThreadLocal on the request out-path and add that call if there's no good reason not to.