debug/dwarf: remove unused field addrsize from Data

The addrsize field is not a constant for an entire executable
file, and is now handled by the dataFormat interface when
reading the data.

R=golang-dev, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/41620043

src/pkg/debug/dwarf/open.go

@@ -24,7 +24,6 @@ type Data struct {
 
 	// parsed data
 	abbrevCache map[uint32]abbrevTable
-	addrsize    int
 	order       binary.ByteOrder
 	typeCache   map[Offset]Type
 	unit        []unit