[XFS] Remove unused header files for MAC and CAP checking functionality.

xfs_mac.h and xfs_cap.h provide definitions and macros that aren't used
anywhere in XFS at all. They are left-overs from "to be implement at some
point in the future" functionality that Irix XFS has. If this
functionality ever goes into Linux, it will be provided at a different
layer, most likely through the security hooks in the kernel so we will
never need this functionality in XFS.

Patch provided by Eric Sandeen (sandeen@sandeen.net).

SGI-PV: 960895
SGI-Modid: xfs-linux-melb:xfs-kern:28036a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>