selftests/damon: remove tests for DAMON debugfs interface

It's time to remove DAMON debugfs interface, which has deprecated long
before in February 2023.  Read the cover letter of this patch series for
more details.

Remove selftests for the interface, to prevent causing unnecessary test
failures.

Link: https://lkml.kernel.org/r/20250106191941.107070-6-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Alex Shi <alexs@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: Hu Haowen <2023002089@link.tyut.edu.cn>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Rae Moar <rmoar@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yanteng Si <si.yanteng@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>