RFR(XS): 8185573: [MVT] Remove references to vgetfield from compiler code

[Tobias Hartmann]

Hi,

https://bugs.openjdk.java.net/browse/JDK-8185573
http://cr.openjdk.java.net/~thartmann/valhalla/vt_prototype/webrev.37/

I removed all references to _vgetfield from compiler code because it's now a VM 
internal bytecode and may not show up in the Java bytecode stream (JDK-8185349).

All tests pass.

Thanks,
Tobias