Remove prefixes from assignment pool examples

[laduke]

Hey, I was pasting in some examples. Some of the ipassignment_pool examples had /24 at the end. terraform plan would then have a diff every time:

resource "zerotier_network" "nightshade" {
        id               = "a0cbf4b62acee046"
        name             = "cattail"
        # (6 unchanged attributes hidden)

      + assignment_pool {
          + end   = "10.1.0.254"
          + start = "10.1.0.1"
        }
      - assignment_pool {
          - end   = "10.1.0.254/24" -> null
          - start = "10.1.0.1/24" -> null
        }

        # (3 unchanged blocks hidden)
    }

I edited this in github. Hope it looks right.