cmd/vet: remove Peek from list of canonical methods

It is insufficiently canonical;
see the discussion at issue 19719.

Fixes #19719

Change-Id: I0559ff3b1b39d7bc4b446d104f36fdf8ce3da50e
Reviewed-on: https://go-review.googlesource.com/38722
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/method.go

@@ -48,7 +48,6 @@ var canonicalMethods = map[string]MethodSig{
 	"GobEncode":     {[]string{}, []string{"[]byte", "error"}},                         // gob.GobEncoder
 	"MarshalJSON":   {[]string{}, []string{"[]byte", "error"}},                         // json.Marshaler
 	"MarshalXML":    {[]string{"*xml.Encoder", "xml.StartElement"}, []string{"error"}}, // xml.Marshaler
-	"Peek":          {[]string{"=int"}, []string{"[]byte", "error"}},                   // image.reader (matching bufio.Reader)
 	"ReadByte":      {[]string{}, []string{"byte", "error"}},                           // io.ByteReader
 	"ReadFrom":      {[]string{"=io.Reader"}, []string{"int64", "error"}},              // io.ReaderFrom
 	"ReadRune":      {[]string{}, []string{"rune", "int", "error"}},                    // io.RuneReader