crypto: doc - remove references to ARC4

arc4 is no longer considered secure, so it shouldn't be used, even as
just an example.  Mention serpent and chacha20 instead.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/crypto/devel-algos.rst

@@ -57,7 +57,7 @@ follows:
 Single-Block Symmetric Ciphers [CIPHER]
 ---------------------------------------
 
-Example of transformations: aes, arc4, ...
+Example of transformations: aes, serpent, ...
 
 This section describes the simplest of all transformation
 implementations, that being the CIPHER type used for symmetric ciphers.
@@ -108,7 +108,7 @@ is also valid:
 Multi-Block Ciphers
 -------------------
 
-Example of transformations: cbc(aes), ecb(arc4), ...
+Example of transformations: cbc(aes), chacha20, ...
 
 This section describes the multi-block cipher transformation
 implementations. The multi-block ciphers are used for transformations