cmd/link: remove some more dead fields from Pcln

Change-Id: Ibb98de29d84a605fb1588c7dc11ad66e3965a137
Reviewed-on: https://go-review.googlesource.com/21223Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>

src/cmd/link/internal/ld/link.go

@@ -240,8 +240,6 @@ type Pcln struct {
 	Funcdata    []*LSym
 	Funcdataoff []int64
 	File        []*LSym
-	Lastfile    *LSym
-	Lastindex   int
 }
 
 type Pcdata struct {