RFR: Aarch64 cleanup

[Roman Kennke]

I'm scrutinizing our JDK9 diff vs. our baseline. Here's some cleanups
for trivial stuff that I found in aarch64:

http://cr.openjdk.java.net/~rkennke/cleanup-aarch64/webrev.01/
<http://cr.openjdk.java.net/%7Erkennke/cleanup-aarch64/webrev.01/>

one is a trivial whitespace change, the other removes code that is dead
because surrounded by #ifdef 0, and the 3rd is removing two
read-barriers in monitorenter/monitorexit that follow a store-check,
which is bogus. There's no read-barriers required there because we
always ensure stuff on the stack is in to-space. That's what the
store-check is checking. We have no read-barriers in the same place in
x86 either.

(Note: I found no bad stuff vs upstream in x86)

Ok?

Roman