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.

config_builder.go

@@ -1096,7 +1096,7 @@ func (d *DefaultDatabaseBuilder) BuildDatabase(
 
 	// The graph store implementation we will use depends on whether
 	// native SQL is enabled or not.
-	var graphStore graphdb.V1Store
+	var graphStore graphdb.Store
 
 	// Instantiate a native SQL store if the flag is set.
 	if d.cfg.DB.UseNativeSQL {