Add helper to remove failed node

[Matt Ludwigs]

Add a helper function in Grizzly.Network module to remove a failed node id

It should wrap this call

Grizzly.send_command(1, :failed_node_remove, node_id: node_id, seq_number: seq_number)

Where node_id is passed into the function by the caller and the seq_number is from the Grizzly.SeqNumber.get_and_inc/0 function.

[Ben Youngblood]

This is done -- see Grizzly.Network.remove_failed_node/1.