remove TODO from external_source.sql

deployment/postgres-init-db/sql/tables/merlin/external_events/external_source.sql

@@ -13,8 +13,6 @@ create table merlin.external_source (
       primary key (key, derivation_group_name),
     -- a given dg cannot have two sources with the same valid_at!
     CONSTRAINT dg_unique_valid_at UNIQUE (derivation_group_name, valid_at),
-    -- TODO: going forward, we might want to consider making an exception to the above if sources have no overlap. That
-    --        being said, this may be overkill or an unnecessary complication to the general rule.
     constraint external_source_references_external_source_type_name
       foreign key (source_type_name)
       references merlin.external_source_type(name),