dma-buf: Remove DMA-BUF sysfs stats

dma-buf: Remove DMA-BUF sysfs stats

Commit bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF stats
in sysfs") added dmabuf statistics to sysfs in 2021 under
CONFIG_DMABUF_SYSFS_STATS. After being used in production, performance
problems were discovered leading to its deprecation in 2022 in commit
e0a9f1fe206a ("dma-buf: deprecate DMABUF_SYSFS_STATS"). Some of the
problems with this interface were discussed in my LPC 2025 talk. [1][2]

Android was probably the last user of the interface, which has since
been migrated to use the dmabuf BPF iterator [3] to obtain the same
information more cheaply. As promised in that series, now that the
longterm stable 6.18 kernel has been released let's remove the sysfs
dmabuf statistics from the kernel.

[1] https://www.youtube.com/watch?v=D83qygudq9c
[2] https://lpc.events/event/19/contributions/2118/
[3] https://lore.kernel.org/all/20250522230429.941193-1-tjmercier@google.com/

Signed-off-by: T.J. Mercier <tjmercier@google.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patch.msgid.link/20260116190517.3268458-1-tjmercier@google.com