RFR: 8156768: [JVMCI] remove support for patching Symbol pointers

[Roland Schatz]

Hi,

Please review this change:
http://cr.openjdk.java.net/~rschatz/JDK-8156768/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8156768

This is a followup on https://bugs.openjdk.java.net/browse/JDK-8155735, 
removing the stuff that's now unused.

Thanks,
Roland