The conversion was done with an automated tool and then
modified only as necessary to make it compile and run.

vlrt.c was only called from C. Pure delete.

[This CL is part of the removal of C code from package runtime.
See golang.org/s/dev.cc for an overview.]

LGTM=r
R=r, austin
CC=dvyukov, golang-codereviews, iant, khr
https://golang.org/cl/174860043