go/ssa: fix stale docs for CreateProgram and Build

Both functions had documentation referring to BuildAll when the
function is now called Build.

Change-Id: I59cce397a0a72bf7fa36f9798e2b07bb6b1da726
Reviewed-on: https://go-review.googlesource.com/25084
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2 files changed