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>
Disable encrypt them mac for SSL 3.0 and stream ciphers (RC4 only).

Reviewed-by: Tim Hudson <tjh@openssl.org>
Remove reference to deleted md4.c

Reviewed-by: Kurt Roeckx <kurt@openssl.org>