go/ssa: use ast.RangeStmt.Range position directly

ast.RangeStmt.Range has been available since 1.20.

Change-Id: Ia3f9b3075d39c6415e20dfdb3151e94fbf11a597
Reviewed-on: https://go-review.googlesource.com/c/tools/+/614458
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: timothy-king

go/ssa/builder.go

@@ -2508,7 +2508,7 @@ func (b *builder) rangeFunc(fn *Function, x Value, tk, tv types.Type, rng *ast.R
 		name:           fmt.Sprintf("%s$%d", fn.Name(), anonIdx+1),
 		Signature:      ysig,
 		Synthetic:      "range-over-func yield",
-		pos:            rangePosition(rng),
+		pos:            rng.Range,
 		parent:         fn,
 		anonIdx:        int32(len(fn.AnonFuncs)),
 		Pkg:            fn.Pkg,

go/ssa/util.go

@@ -44,13 +44,6 @@ func isBlankIdent(e ast.Expr) bool {
 	return ok && id.Name == "_"
 }
 
-// rangePosition is the position to give for the `range` token in a RangeStmt.
-var rangePosition = func(rng *ast.RangeStmt) token.Pos {
-	// Before 1.20, this is unreachable.
-	// rng.For is a close, but incorrect position.
-	return rng.For
-}
-
 //// Type utilities.  Some of these belong in go/types.
 
 // isNonTypeParamInterface reports whether t is an interface type but not a type parameter.