Revert "Test suite: wait for the remote shell a bit longer after restoring a snapshot."

This reverts commit 8405ba21.

Waiting longer doesn't help:

  [...]
  Restoring snapshot 'no-network-logged-in'...
  Remote shell: calling as root: echo 'hello?'
  The remote shell failed to respond within 30 seconds
  The remote shell is down after restoring snapshot. Retrying... (attempt 1 of 3)
  [...]