Kernel builders could silently enable CONFIG_DAMON_DBGFS_DEPRECATED. 
Users who manually check the files under the DAMON debugfs directory could
notice the deprecation owing to the 'DEPRECATED' DAMON debugfs file, but
there could be users who doesn't manually check the files.

Make the deprecation cannot be ignored in the case by renaming
'monitor_on' file, which is essential for real use of DAMON on runtime, to
'monitor_on_DEPRECATED'.  Still users who control DAMON via only
user-space tool could ignore the deprecation, but that's what the tool
developers should take care of.  DAMON user-space tool, damo, has also
made a change[1] for the purpose.

[1] commit 935dae76f2aee ("_damon_args: Rename --damon_interface to
    --damon_interface_DEPRECATED") of https://github.com/awslabs/damo

Link: https://lkml.kernel.org/r/20240130013549.89538-8-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Alex Shi <alexs@kernel.org>
Cc: Hu Haowen <2023002089@link.tyut.edu.cn>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>