revert recent lib changes (#476)

## Issue
Previous changes made it so that on Mongos-K8s would return different
endpoints to inside K8s apps and outside k8s apps if expose-external
enabled.

However it was decided recently that this approach is incorrect.

## Solution

Revert this change and bump libpatch

lib/charms/mongodb/v1/mongodb_provider.py

@@ -31,7 +31,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 12
+LIBPATCH = 13
 
 logger = logging.getLogger(__name__)
 REL_NAME = "database"
@@ -303,9 +303,7 @@ def _get_config(self, username: str, password: Optional[str]) -> MongoConfigurat
         if self.charm.is_role(Config.Role.MONGOS):
             mongo_args["port"] = Config.MONGOS_PORT
             if self.substrate == Config.Substrate.K8S:
-                external = self.is_external_client(relation.id)
-                mongo_args["port"] = self.charm.get_mongos_port(external)
-                mongo_args["hosts"] = self.charm.get_mongos_hosts(external)
+                mongo_args["port"] = self.charm.get_mongos_port()
         else:
             mongo_args["replset"] = self.charm.app.name
 
@@ -401,13 +399,6 @@ def get_relation_name(self):
         else:
             return REL_NAME
 
-    def is_external_client(self, rel_id) -> bool:
-        """Returns true if the integrated client requests external connectivity."""
-        return (
-            self.database_provides.fetch_relation_field(rel_id, EXTERNAL_CONNECTIVITY_TAG)
-            == "true"
-        )
-
     @staticmethod
     def _get_database_from_relation(relation: Relation) -> Optional[str]:
         """Return database name from relation."""