go/ast/inspector: remove obsolete unsafe import

It should have been removed when we deleted the use of linkname.

Also, add a postscript to a comment. Sadly I can't find the data.

Change-Id: I05518a770b941a4f361f6ce7b80fc1b5bc94eab9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/694056
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>

Author: adonovan

go/ast/inspector/inspector.go

@@ -85,6 +85,7 @@ type event struct {
 
 // TODO: Experiment with storing only the second word of event.node (unsafe.Pointer).
 // Type can be recovered from the sole bit in typ.
+// [Tried this, wasn't faster. --adonovan]
 
 // Preorder visits all the nodes of the files supplied to New in
 // depth-first order. It calls f(n) for each node n before it visits

go/ast/inspector/typeof.go

@@ -12,8 +12,6 @@ package inspector
 import (
 	"go/ast"
 	"math"
-
-	_ "unsafe"
 )
 
 const (