It's a bug to have a type with both the file_type and fs_type
attribute. A type should be declared with either file_type,
or fs_type, but not both.

Create a neverallow rule which detects this situation. This works
because we have the following allow rule:

  allow fs_type self:filesystem associate;

If a type is a file_type and an fs_type, the associate allow rule
will conflict with this neverallow rule.

Not sure if this is the cleanest way to accomplish this, but it
seems to work.

Change-Id: Ida387b1df260efca15de38ae7a66ed25e353acaa