[foreign-memaccess] RFR 8225720: Cleanup var handle address generation with byte carriers

[Maurizio Cimadamore]

Hi,
the template for var handle memaccess generation has some leftovers from 
when we did bit swapping on 'byte' carriers. We have removed that in 
[1], so we can now clean up the code for good.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8225720/

Maurizio

[1] - 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-May/005597.html