Remove notes about MongoDB

There's no MongoDB anymore anywhere.

Change-Id: Id6f912b48d6c36478ef8db9a08bd3502ed94eb2f

aodh/tests/functional/gabbi/gabbits/capabilities.yaml

@@ -7,7 +7,6 @@ fixtures:
 tests:
 
 - name: get capabilities
-  desc: retrieve capabilities for the mongo store
   url: /v2/capabilities
   response_json_paths:
       $.alarm_storage.['storage:production_ready']: true

doc/source/webapi/v2.rst

@@ -62,16 +62,6 @@ and *AlarmChange*. The following comparison operators are supported: *=*, *!=*,
 *and* *or* and *not*. The field names are validated against the database
 models.
 
-.. note:: The *not* operator has different meaning in Mongo DB and in SQL DB engine.
-   If the *not* operator is applied on a non existent metadata field then
-   the result depends on the DB engine. For example, if
-   {"not": {"metadata.nonexistent_field" : "some value"}} filter is used in a query
-   the Mongo DB will return every Sample object as *not* operator evaluated true
-   for every Sample where the given field does not exists. See more in the Mongod DB doc.
-   On the other hand, SQL based DB engine will return empty result as the join operation
-   on the metadata table will return zero rows as the on clause of the join which
-   tries to match on the metadata field name is never fulfilled.
-
 Complex Query supports defining the list of orderby expressions in the form
 of [{"field_name": "asc"}, {"field_name2": "desc"}, ...].