staging: slicoss: remove gratuitous debug infrastructure

As per the TODO file, this patch removes the gratuitous debug
infrastructure. As an extra incentive for removing this code,
the debugfs files are not cleaned up properly. For example, if
register_netdev() fails in slic_entry_probe() then all debugfs
files get left behind, even after the driver module is unloaded.
Touching these files quickly leads to an oops.

Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>