when executing `destroy_all` on an embedded association, the `$pullAll` operator might not work if the content of the relation was changed. the change might be just order of the values in one of the embedded objects, which will cause the operation to not delete anything.

for example, say I have the following models

class Parent
   include Mongoid::Document
   embeds_many :blocks
end

class Block
   include Mongoid::Document
   field :name, type: String
   embeds_many :children
end

class Child
   include Mongoid::Document
   embedded_in :block
  
   field :size, type: Integer
   field :order, type: Integer
   field :t
end

Mongo::Logger.logger=Logger.new(STDERR)
Mongo::Logger.logger.level=Logger::DEBUG


parent = Parent.new
parent.blocks << Block.new(name: 'test', children: [size: 1, order: 1])
parent.save!

Now, I'll update the attributes of the child, switching the attributes order

# this is just an example
parent.blocks[0].children[0].assign_attributes(size: 2)

now, a `$pullAll` command will be generate with an element such as `blocks: [\{_id: ObjectId(...), order: 1, size: 1}]` however, mongo still has the object as `{size: 1, order: 1}`, and will fail to find it and delete it

parent.blocks.destroy_all(:name => 'test')

 why not using a `$pull` command and query it by the `_id` of the matched elements?