Adapt to swh.core 2.0.0

- add the `get_datastore` function in `swh.indexer`
- add the `get_current_version` method in `IndexerBackend`,
- remove dbversion management from sql init script
- update tests accordingly

swh/indexer/__init__.py

-# Copyright (C) 2016-2018  The Software Heritage developers
+# Copyright (C) 2016-2022  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
+
+
+# implemented as a function to help lazy loading
+def get_datastore(*args, **kw):
+    from .indexer import get_indexer_storage
+
+    return get_indexer_storage(*args, **kw)

swh/indexer/sql/30-schema.sql

@@ -2,19 +2,6 @@
 --- Software Heritage Indexers Data Model
 ---
 
--- drop schema if exists swh cascade;
--- create schema swh;
--- set search_path to swh;
-
-create table dbversion
-(
-  version     int primary key,
-  release     timestamptz,
-  description text
-);
-
-insert into dbversion(version, release, description)
-      values(133, now(), 'Work In Progress');
 -- Computing metadata on sha1's contents
 
 -- a SHA1 checksum (not necessarily originating from Git)