cifs: version operations for smb20 unneeded when legacy support disabled

We should not be including unused smb20 specific code when legacy
support is disabled (CONFIG_CIFS_ALLOW_INSECURE_LEGACY turned
off).  For example smb2_operations and smb2_values aren't used
in that case.  Over time we can move more and more SMB1/CIFS and SMB2.0
code into the insecure legacy ifdefs

Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>