Revert "Enable symmetric difference for LoLs"

This reverts commit e76350b4c01a0df0209727ab2635290dde99e478.

The Baggy version doesn't really make sense in the end.
Another go at LoL-ifying the symmetric difference operator

This may still not be the optimal solution for bags, but you can read on for
details of different approaches:

  # Using colomon's suggestion
  # (which makes me believe there must be a list op-y way to declare this.. would
  # it be the same statement for both lists and bags?
  #   ([(|)] @p) (-) ([(&)] @p)
  #
  > [(^)] (44,3,2,1,5,77),(3,2),(1,5)
  set(44, 3, 2, 1, 5, 77)
  > [(^)] (44,3,3,3,2,2,2,1,5,77,77,77,777).Bag,(3,2,77).Bag,(1,5,5).Bag
  bag(44, 3(3), 2(3), 1, 5(2), 77(3), 777)

  # my contribution, in camelia-speak
      m: my $a = bag 88,88,88,4,3,3,1,3,88; my $b = bag 88,4,3; my $i = $a (|) $b; my
      $nw = BagHash.new; for $i.keys -> $k { $nw{$k} = $a{$k} - $b{$k} }; $nw.say

      <+camelia> rakudo-moar 914434: OUTPUT<<BagHash.new(88(3), 3(2), 1)[NL]>>

  # translating that to the (^) operator, my algorithm reveals a weakness. it
  # breaks on the 5s in the last list, the bag doesn't do a negative value
  > [(^)] (44,3,3,3,2,2,2,1,5,77,77,77,777).Bag,(3,2,77).Bag,(1,5,5).Bag
  bag(44, 3(2), 2(2), 5, 77(2), 777)

  # here we take the absolute value of the subtraction, so that the difference is
  # distributed based on new lists. This could arguably be considered "commutative".
  > [(^)] (44,3,3,3,2,2,2,1,5,77,77,77,777).Bag,(3,2,77).Bag,(1,2,44,5,5,5).Bag
  bag(3(2), 2, 5(2), 77(2), 777)

Another approach could be to set the existing baghash key's value to zero if
the next bag's value for that key is 'greater than'. This doesn't feel
very cumulative though--if an unset key reappears, the baghash will take the
value from that key's respective list without regard for any previous
lists.