Drop process state at `done`.

The `cowboy` connection spawns process per connection.
No pools connection, pools acceptor.  If keep old approach,
`server_status_client:working/1`, and `server_status_client:done/0`
are called from acceptor.  But there is no hook.

Now, server_status shows only `working` processes.  Not includes
`done` processes.
Add `method` property.