Remove d2i_DHparams.pod and move documentation to d2i_RSAPrivateKey.pod

d2i_RSAPrivateKey.pod is the more generic page for these deprecated
functions and provides advice and guidance on how to translate the old
style functions into new ones.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13138)

doc/man3/d2i_DHparams.pod

@@ -1,42 +0,0 @@
-=pod
-
-=head1 NAME
-
-d2i_DHparams, i2d_DHparams - PKCS#3 DH parameter functions
-
-=head1 SYNOPSIS
-
- #include <openssl/dh.h>
-
- DH *d2i_DHparams(DH **a, const unsigned char **pp, long length);
- int i2d_DHparams(DH *a, unsigned char **pp);
-
-=head1 DESCRIPTION
-
-These functions decode and encode PKCS#3 DH parameters using the
-DHparameter structure described in PKCS#3.
-
-Otherwise these behave in a similar way to d2i_X509() and i2d_X509()
-described in the L<d2i_X509(3)> manual page.
-
-=head1 RETURN VALUES
-
-d2i_DHparams() returns a valid B<DH> structure or NULL if an error occurred.
-
-i2d_DHparams() returns the length of encoded data on success or a value which
-is less than or equal to 0 on error.
-
-=head1 SEE ALSO
-
-L<d2i_X509(3)>
-
-=head1 COPYRIGHT
-
-Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
-
-Licensed under the Apache License 2.0 (the "License").  You may not use
-this file except in compliance with the License.  You can obtain a copy
-in the file LICENSE in the source distribution or at
-L<https://www.openssl.org/source/license.html>.
-
-=cut

doc/man3/d2i_RSAPrivateKey.pod

@@ -2,7 +2,7 @@
 
 =begin comment
 
-Any deprecated keypair function from d2i_X509.pod are collected in this file.
+Any deprecated keypair/params d2i or i2d functions are collected on this page.
 
 =end comment
 
@@ -17,6 +17,9 @@ d2i_RSAPublicKey_fp,
 d2i_RSA_PUBKEY,
 d2i_RSA_PUBKEY_bio,
 d2i_RSA_PUBKEY_fp,
+d2i_DHparams,
+d2i_DHparams_bio,
+d2i_DHparams_fp,
 i2d_RSAPrivateKey,
 i2d_RSAPrivateKey_bio,
 i2d_RSAPrivateKey_fp,
@@ -25,7 +28,10 @@ i2d_RSAPublicKey_bio,
 i2d_RSAPublicKey_fp,
 i2d_RSA_PUBKEY,
 i2d_RSA_PUBKEY_bio,
-i2d_RSA_PUBKEY_fp
+i2d_RSA_PUBKEY_fp,
+i2d_DHparams,
+i2d_DHparams_bio,
+i2d_DHparams_fp
 - DEPRECATED
 
 =head1 SYNOPSIS