Cleanup stale device lists for users we don't share a room with anymore (#2857)

The stale device lists table might contain entries for users we don't
share a room with anymore. This now asks the roomserver about left users
and removes those entries from the table.

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

keyserver/keyserver_test.go

@@ -0,0 +1,29 @@
+package keyserver
+
+import (
+	"context"
+	"testing"
+
+	roomserver "github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/test"
+	"github.com/matrix-org/dendrite/test/testrig"
+)
+
+type mockKeyserverRoomserverAPI struct {
+	leftUsers []string
+}
+
+func (m *mockKeyserverRoomserverAPI) QueryLeftUsers(ctx context.Context, req *roomserver.QueryLeftUsersRequest, res *roomserver.QueryLeftUsersResponse) error {
+	res.LeftUsers = m.leftUsers
+	return nil
+}
+
+// Merely tests that we can create an internal keyserver API
+func Test_NewInternalAPI(t *testing.T) {
+	rsAPI := &mockKeyserverRoomserverAPI{}
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		base, closeBase := testrig.CreateBaseDendrite(t, dbType)
+		defer closeBase()
+		_ = NewInternalAPI(base, &base.Cfg.KeyServer, nil, rsAPI)
+	})
+}