Documentation typo fix in EVP_EncryptInit.pod

Remove duplicate declaration of `EVP_CIPHER_key_length` in the synopsis.

CLA: trivial
Reviewed-by: NAndy Polyakov <appro@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5792)

doc/man3/EVP_EncryptInit.pod

@@ -99,7 +99,6 @@ EVP_enc_null
 
  int EVP_CIPHER_nid(const EVP_CIPHER *e);
  int EVP_CIPHER_block_size(const EVP_CIPHER *e);
- int EVP_CIPHER_key_length(const EVP_CIPHER *e)
  int EVP_CIPHER_key_length(const EVP_CIPHER *e);
  int EVP_CIPHER_iv_length(const EVP_CIPHER *e);
  unsigned long EVP_CIPHER_flags(const EVP_CIPHER *e);