docs: admin-guide/blockdev: Remove digraph of node-states

While node-states-8.dot has two digraphs, the dot(1) command can
not properly handle multiple graphs in a DOT file and the
kernel-doc page a

docs: admin-guide/blockdev: Remove digraph of node-states

While node-states-8.dot has two digraphs, the dot(1) command can
not properly handle multiple graphs in a DOT file and the
kernel-doc page at

https://www.kernel.org/doc/html/latest/admin-guide/blockdev/drbd/figures.html

fails to render the graphs.

It turned out that the digraph of node_states can be removed.

Quote from Joel's reflection:

On reflection, the digraph node_states can be removed entirely.
It is too basic to contain any useful information. In addition
it references "ioctl_set_state". The ioctl configuration
interface for DRBD has long been removed. In fact, it was never
in the upstream version of DRBD.

Remove node_states and rename the DOT file peer_states-8.dot.

Suggested-by: Joel Colledge <[email protected]>
Acked-by: Joel Colledge <[email protected]>
Signed-off-by: Akira Yokosawa <[email protected]>
Cc: Philipp Reisner <[email protected]>
Cc: Lars Ellenberg <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>

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