cmd/internal/obj: remove Link.Version

It is zeroed pointlessly and never read.

Change-Id: I65390501a878f545122ec558cb621b91e394a538
Reviewed-on: https://go-review.googlesource.com/40406
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/internal/obj/link.go

@@ -728,7 +728,6 @@ type Link struct {
 	Plan9privates *LSym
 	DiagFunc      func(string, ...interface{})
 	DebugInfo     func(fn *LSym, curfn interface{}) []*dwarf.Var // if non-nil, curfn is a *gc.Node
-	Version       int
 	Errors        int
 
 	Framepointer_enabled bool

src/cmd/internal/obj/sym.go

@@ -55,7 +55,6 @@ func Linknew(arch *LinkArch) *Link {
 	ctxt := new(Link)
 	ctxt.Hash = make(map[SymVer]*LSym)
 	ctxt.Arch = arch
-	ctxt.Version = 0
 	ctxt.Pathname = WorkingDir()
 
 	ctxt.Headtype.Set(GOOS)