cmd/compile: remove Label.Link field and lastlabel global var

Change-Id: If2a174f482ecd56dee43f921d13fef98439872fc
Reviewed-on: https://go-review.googlesource.com/20559
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index 4bf7385..c98637c 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -86,10 +86,9 @@
 }
 
 type Label struct {
-	Sym  *Sym
-	Def  *Node
-	Use  []*Node
-	Link *Label
+	Sym *Sym
+	Def *Node
+	Use []*Node
 
 	// for use during gen
 	Gotopc   *obj.Prog // pointer to unresolved gotos