crypto: ansi_cprng - Remove unused ansi_cprng algorithm

Remove ansi_cprng, since it's obsolete and unused, as confirmed at
https://lore.kernel.org/r/aQxpnckYMgAAOLpZ@gondor.apana.org.au/

This was originally added in 2008, apparently as a FIPS approved random
number generator.  Whether this has ever belonged upstream is
questionable.  Either way, ansi_cprng is no longer usable for this
purpose, since it's been superseded by the more modern algorithms in
crypto/drbg.c, and FIPS itself no longer allows it.  (NIST SP 800-131A
Rev 1 (2015) says that RNGs based on ANSI X9.31 will be disallowed after
2015.  NIST SP 800-131A Rev 2 (2019) confirms they are now disallowed.)

Therefore, there is no reason to keep it around.

Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Haotian Zhang <vulab@iscas.ac.cn>
Cc: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/crypto/userspace-if.rst

@@ -302,10 +302,9 @@ follows:
 
 
 Depending on the RNG type, the RNG must be seeded. The seed is provided
-using the setsockopt interface to set the key. For example, the
-ansi_cprng requires a seed. The DRBGs do not require a seed, but may be
-seeded. The seed is also known as a *Personalization String* in NIST SP 800-90A
-standard.
+using the setsockopt interface to set the key. The SP800-90A DRBGs do
+not require a seed, but may be seeded. The seed is also known as a
+*Personalization String* in NIST SP 800-90A standard.
 
 Using the read()/recvmsg() system calls, random numbers can be obtained.
 The kernel generates at most 128 bytes in one call. If user space