x/tools/go/ssa: remove unused field from NamedConst

Found with honnef.co/go/tools/cmd/unused.

Change-Id: I68b4af07cc64a46f5794a0e339859f4d6bc9dad1
Reviewed-on: https://go-review.googlesource.com/37605
Reviewed-by: Alan Donovan <adonovan@google.com>
diff --git a/go/ssa/ssa.go b/go/ssa/ssa.go
index a8bcbb6..e8350f1 100644
--- a/go/ssa/ssa.go
+++ b/go/ssa/ssa.go
@@ -92,7 +92,6 @@
 type NamedConst struct {
 	object *types.Const
 	Value  *Const
-	pos    token.Pos
 	pkg    *Package
 }