cmd/internal/obj: shrink Prog, remove two unused fields

Printed and Width were unused.

Despite only removing two bytes, due to alignment, 8 bytes are saved
on 64-bit:

Before: unsafe.Sizeof(obj.Prog{}) == 304
 After: unsafe.Sizeof(obj.Prog{}) == 296

The next size class below 320 (304=>19(320)) is 288. Still 8 bytes
away from that.

Change-Id: I8d1632dd40d387f7036c03c65ea4d64e9b6218c3
Reviewed-on: https://go-review.googlesource.com/10511
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/internal/obj/link.go

@@ -224,8 +224,6 @@ type Prog struct {
 	Ft       uint8
 	Tt       uint8
 	Isize    uint8
-	Printed  uint8
-	Width    int8
 	Mode     int8
 
 	Info ProgInfo