sysv: Remove the filesystem

sysv: Remove the filesystem

Since 2002 (change "Replace BKL for chain locking with sysvfs-private
rwlock") the sysv filesystem was doing IO under a rwlock in its
get_block() function (yes, a non-sleepable lock hold over a function
used to read inode metadata for all reads and writes).  Nobody noticed
until syzbot in 2023 [1]. This shows nobody is using the filesystem.
Just drop it.

[1] https://lore.kernel.org/all/0000000000000ccf9a05ee84f5b0@google.com/

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20250220163940.10155-2-jack@suse.cz
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>