Removed duplicate definition of PKCS7_type_is_encrypted

Patch supplied by Matthieu Patou <mat@matws.net>, and modified to also
remove duplicate definition of PKCS7_type_is_digest.

PR#3551

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit e0fdea3e49e7454aa76bd5ecf3a3747641354c68)