cifs: More crypto cleanup (try #2)

Replaced md4 hashing function local to cifs module with kernel crypto APIs.
As a result, md4 hashing function and its supporting functions in
file md4.c are not needed anymore.

Cleaned up function declarations, removed forward function declarations,
and removed a header file that is being deleted from being included.

Verified that sec=ntlm/i, sec=ntlmv2/i, and sec=ntlmssp/i work correctly.

Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>