runtime: remove the dummy arg of getcallersp

This is a port of https://golang.org/cl/109596 to the gofrontend, in
preparation for updating libgo to 1.11.

Original CL description:

    getcallersp is intrinsified, and so the dummy arg is no longer
    needed. Remove it, as well as a few dummy args that are solely
    to feed getcallersp.

Change-Id: Ib9c3714c8c6faf4b898799f398df54391b53ef60
Reviewed-on: https://go-review.googlesource.com/131116
Reviewed-by: Cherry Zhang <cherryyz@google.com>