x/tools: remove old renaming imports of go/constant as exact

Fixes golang/go#26522

Change-Id: Ie8184a358f11bc7ad855e0eeb964c29848d2263e
Reviewed-on: https://go-review.googlesource.com/128998
Run-TryBot: Alan Donovan <adonovan@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/go/ssa/ssa.go b/go/ssa/ssa.go
index 7cde827..7f7998a 100644
--- a/go/ssa/ssa.go
+++ b/go/ssa/ssa.go
@@ -10,7 +10,7 @@
 import (
 	"fmt"
 	"go/ast"
-	exact "go/constant"
+	"go/constant"
 	"go/token"
 	"go/types"
 	"sync"
@@ -404,9 +404,8 @@
 // All source-level constant expressions are represented by a Const
 // of the same type and value.
 //
-// Value holds the exact value of the constant, independent of its
-// Type(), using the same representation as package go/exact uses for
-// constants, or nil for a typed nil value.
+// Value holds the value of the constant, independent of its Type(),
+// using go/constant representation, or nil for a typed nil value.
 //
 // Pos() returns token.NoPos.
 //
@@ -417,7 +416,7 @@
 //
 type Const struct {
 	typ   types.Type
-	Value exact.Value
+	Value constant.Value
 }
 
 // A Global is a named Value holding the address of a package-level
@@ -658,7 +657,7 @@
 // of X, and Program.Method(m) to find the implementation of a method.
 //
 // To construct the zero value of an interface type T, use:
-// 	NewConst(exact.MakeNil(), T, pos)
+// 	NewConst(constant.MakeNil(), T, pos)
 //
 // Pos() returns the ast.CallExpr.Lparen, if the instruction arose
 // from an explicit conversion in the source.