One way to do it

# We are modifying the $/ variable, so we limit the scope
# by adding some {} around the code
{
  local $/ = '';
  $^I      = '.bak';  # See man perl and the -i switch for that trick
  @ARGV    = ('data.txt');
  while (<>) {
    # The order is not important, so we sort the fields to
    # obtain a unique id
    $sorted = join ':', sort split /\s+/; 
    print if (! $seen{$sorted}++ );
  }
}
[download]

HTH
Update : add comments to the code
--
zejames