vfmt: remove rc4.v from known_failing_exceptions

cmd/tools/vtest-fmt.v

@@ -8,7 +8,6 @@ import v.util
 const (
 	known_failing_exceptions = [
 		'vlib/crypto/aes/const.v', // multiple narrow columns of []string turned to 1 long single column, otherwise works
-		'vlib/crypto/rc4/rc4.v', // pub fn (mut c Cipher) xor_key_stream(mut dst, mut src []byte) {
 		'vlib/vweb/vweb.v', // $for method in T.methods { => $for method in T(methods) { , `return // xx` => parse expr error
 		'vlib/v/gen/js/tests/life.v', // error: unexpected `,`, expecting ), on JS.setInterval(fn () { show(game) game = step(game) }, 500)
 		'vlib/builtin/js/builtin.v', // JS.console.error(s) => JS.error(s), JS.process.exit(c) => JS.exit(c)

vlib/crypto/rc4/rc4.v

@@ -1,3 +1,5 @@
+module rc4
+
 // Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
 // Use of this source code is governed by an MIT license
 // that can be found in the LICENSE file.
@@ -8,8 +10,6 @@
 // applications.
 // Based off:   https://github.com/golang/go/blob/master/src/crypto/rc4
 // Last commit: https://github.com/golang/go/commit/b35dacaac57b039205d9b07ea24098e2c3fcb12e
-module rc4
-
 import crypto.internal.subtle
 
 // A Cipher is an instance of RC4 using a particular key.