runtime: remove the dummy arg of getcallersp

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.

    Reviewed-on: https://go-review.googlesource.com/131116

From-SVN: r263840