$last is used to remove dups. $last needs to be set to the $e of this pass to compare it to the $e of the next pass. I suppose you could get rid of $last and do

@array = sort @array;
my $j = -1;
for my $e (@array) {
  if ($j < 0 || $array[$j] ne $e) {
    $array[++$j] = $e;
  }
}
$#array = $j;
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