runtime: replace runtime1.goc with Go and C code

runtime: replace runtime1.goc with Go and C code

    A step toward eliminating goc2c.

    Drop the exported parfor code; it was needed for tests in the past, but
    no longer is. The Go 1.7 runtime no longer uses parfor.

    Reviewed-on: https://go-review.googlesource.com/33324

From-SVN: r242509