MONGOID-5671 [Monkey Patch Removal] Remove Object#blank_criteria? and Hash#__mongoid_unsatisfiable_criteria? (#5700)

* - Remove ``Object#blank_criteria?`` method entirely (was previously deprecated and not used in code.)
- Remove ``Hash#_mongoid_unsatisfiable_criteria?`` method is removed (was previously marked @api private) and move it to a private method of Referenced::HasMany::Enumerable.

* Update enumerable.rb

* removing the specs for unsatisifiable_criteria

this tests an implementation detail and not a behavior, which is
fragile. I'm not even sure this is an implementation detail we want,
and testing it specifically pours metaphorical concrete around it,
making it that much harder to remove later.

---------

Co-authored-by: Jamis Buck <[email protected]>

Author: johnnyshields

source/release-notes/mongoid-9.0.txt

@@ -74,6 +74,7 @@ Deprecated functionality removed
   The method ``Mongoid::QueryCache#clear_cache`` should be replaced with ``Mongo::QueryCache#clear``.
   All other methods and submodules are identically named. Refer to the `driver query cache documentation
   <https://mongodb.com/docs/ruby-driver/current/reference/query-cache/>`_ for more details.
+- ``Object#blank_criteria?`` method is removed (was previously deprecated.)
 
 
 ``touch`` method now clears changed state