Now that HSX is dead we can remove the EnableInvokeDynamic flag and all the legacy code that comes with it. After all it's not possible to run JDK 9 on a VM without invokedynamic support anyway:

$ java -XX:+UnlockDiagnosticVMOptions -XX:-EnableInvokeDynamic
Error occurred during initialization of VM
java/lang/ClassFormatError: This JVM does not support constant tag 18 in class file java/lang/CharSequence