Remove unused get_current_version method

Attribute current_version is already set and directly used by swh db
[version|init|upgrade] clis.

Related to T4305

requirements-swh.txt

-swh.core[db,http] >= 2
+swh.core[db,http] >= 2.9
 swh.storage >= 0.11.1

swh/scheduler/backend.py

@@ -73,9 +73,6 @@ class SchedulerBackend:
             )
             self._db = None
 
-    def get_current_version(self):
-        return self.current_version
-
     def get_db(self):
         if self._db:
             return self._db

[Phabricator Migration user]

Some references in the commit message have been migrated:

• T4305 is now swh-core#4305 (closed)