graph/db: rename V1Store to Store

The underling store will store gossip messages across gossip versions
and we will instead expose version parameters on many of the methods. So
this interface really just abstracts the underlying store/schema type.

graph/db/test_kvdb.go

@@ -10,7 +10,7 @@ import (
 )
 
 // NewTestDB is a helper function that creates an BBolt database for testing.
-func NewTestDB(t testing.TB) V1Store {
+func NewTestDB(t testing.TB) Store {
 	backend, backendCleanup, err := kvdb.GetTestBackend(t.TempDir(), "cgr")
 	require.NoError(t, err)