RFR (XS) 8068317: No_Safepoint_Verifier is not necessary in Rewriter::scan_method

[coleen.phillimore at oracle.com]

Summary: remove NSV, Method* can't move or be redefined while being 
rewritten

One down, lots more to look at.

open webrev at http://cr.openjdk.java.net/~coleenp/8068317.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8068317

Tested with tier1 testing on linux/x64.  Will run JPRT.

Thanks,
Coleen