NR_WRITEBACK_TEMP removal

The removal of the counter is straightforward. The reason for the large
Cc list is that there is a comment in mm/page-writeback.c function
wb_position_ratio() that mentions NR_WRITEBACK_TEMP, and just deleting
the sentence feels to me it could be the wrong thing to do - maybe the
strictlimit feature itself is now obsolete? It sure does mention FUSE
as the main reason to exist, but commit 5a53748568f79 that introduced it
also mentions slow USB sticks as a possibile scenario. Has that
happened? I'm not familiar enough with this so I'd rather highlight this
and ask for input here than make "git grep NR_WRITEBACK_TEMP" return
nothing.

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To: Andrew Morton <akpm@linux-foundation.org>
To: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@fb.com>
Cc: Maxim Patlasov <mpatlasov@parallels.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Zach O'Keefe <zokeefe@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joanne Koong <joannelkoong@gmail.com>
Cc: Jingbo Xu <jefflexu@linux.alibaba.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-mm@kvack.org
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

---
Changes in v2:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v1: https://patch.msgid.link/20250625-nr_writeback_removal-v1-1-7f2a0df70faa@suse.cz



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    "change-id": "20250625-nr_writeback_removal-4eca139cf09a",
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