Revert "cmd/vet: teach vet about ast.AliasSpec"

This reverts commit aa8c8e77.

Reason: Decision to back out current alias implementation.

For #16339.

Change-Id: I4db9a8d6b3625c794be9d2f1ff0e9c047f383d28
Reviewed-on: https://go-review.googlesource.com/32827
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Chris Manghane <cmang@golang.org>

src/cmd/vet/copylock.go

@@ -61,10 +61,7 @@ func checkCopyLocksGenDecl(f *File, gd *ast.GenDecl) {
 		return
 	}
 	for _, spec := range gd.Specs {
-		valueSpec, ok := spec.(*ast.ValueSpec)
-		if !ok {
-			continue
-		}
+		valueSpec := spec.(*ast.ValueSpec)
 		for i, x := range valueSpec.Values {
 			if path := lockPathRhs(f, x); path != nil {
 				f.Badf(x.Pos(), "variable declaration copies lock value to %v: %v", valueSpec.Names[i].Name, path)

src/cmd/vet/shadow.go

@@ -188,7 +188,8 @@ func checkShadowDecl(f *File, d *ast.GenDecl) {
 	for _, spec := range d.Specs {
 		valueSpec, ok := spec.(*ast.ValueSpec)
 		if !ok {
-			continue
+			f.Badf(spec.Pos(), "invalid AST: var GenDecl not ValueSpec")
+			return
 		}
 		// Don't complain about deliberate redeclarations of the form
 		//	var i = i

src/cmd/vet/testdata/copylock.go

 package testdata
 
 import (
-	"runtime"
 	"sync"
 	"sync/atomic"
 )
@@ -157,11 +156,3 @@ func AtomicTypesCheck() {
 	vP := &vX
 	vZ := &atomic.Value{}
 }
-
-// ensure we don't crash when we encounter aliases; issue 17755
-
-var _ => runtime.MemProfileRate
-
-const _ => runtime.Compiler
-
-type _ => sync.Mutex