Correct EVP_CIPHER_meth_new.pod and EVP_MD_meth_new.pod

One had some lines copied from the other, and both were missing a
proper RETURN VALUES section.

Fixes #4781

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4787)

(cherry picked from commit 51e47d5f)