media: atomisp: Remove unused atomisp_css_get_dis_statistics()

Remove the unused atomisp_css_get_dis_statistics() function. This seems to
be a leftover variant / older version of atomisp_css_get_dis_stats() which
is actually used.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>