doc: remove reference to the predecessor of SHA-1.

Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12322)

doc/man3/SHA256_Init.pod

@@ -79,9 +79,6 @@ SHA512_DIGEST_LENGTH). Also note that, as for the SHA1() function above, the
 SHA224(), SHA256(), SHA384() and SHA512() functions are not thread safe if
 B<md> is NULL.
 
-The predecessor of SHA-1, SHA, is also implemented, but it should be
-used only when backward compatibility is required.
-
 =head1 RETURN VALUES
 
 SHA1(), SHA224(), SHA256(), SHA384() and SHA512() return a pointer to the hash