cmd/compile: remove references to *gc.Node in docs
ssa.Sym is only implemented by *ir.Name or *obj.LSym.
Change-Id: Ia171db618abd8b438fcc2cf402f40f3fe3ec6833
Reviewed-on: https://go-review.googlesource.com/c/go/+/660995
Auto-Submit: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>