gofmt: remove redundant check in rewriter

If the actual types of two reflect values are
the same and the values are structs, they must
have the same number of fields.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/108280043

src/cmd/gofmt/rewrite.go

@@ -226,9 +226,6 @@ func match(m map[string]reflect.Value, pattern, val reflect.Value) bool {
 		return true
 
 	case reflect.Struct:
-		if p.NumField() != v.NumField() {
-			return false
-		}
 		for i := 0; i < p.NumField(); i++ {
 			if !match(m, p.Field(i), v.Field(i)) {
 				return false