kernfs: remove redundant kernfs_rwsem declaration.

kernfs: remove redundant kernfs_rwsem declaration.

Since 'commit 393c3714081a ("kernfs: switch global kernfs_rwsem lock to
per-fs lock")' per-fs kernfs_rwsem has replaced global kernfs_rwsem.
Remove redundant declaration of global kernfs_rwsem.

Fixes: 393c3714081a ("kernfs: switch global kernfs_rwsem lock to per-fs lock")
Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Link: https://lore.kernel.org/r/20220218010205.717582-1-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>