Event trigger cstore_ddl_event_end,cstore_drop_event created and not owned by extension

Hi,

we have cstore_fwd 1.5, and we tried pg_dump/restore and there was error when we try restore.
```
\dx
List of installed extensions
Name | Version | Schema | Description
-------------------+------------------+-------------------+------------------------------------------------------
cstore_fdw | 1.5 | public | foreign-data wrapper for flat cstore access
```
```
\dx+ cstore_fdw
Objects in extension "cstore_fdw"
Object description
--------------------------------------------
foreign-data wrapper cstore_fdw
function cstore_clean_table_resources(oid)
function cstore_ddl_event_end_trigger()
function cstore_drop_trigger()
function cstore_fdw_handler()
function cstore_fdw_validator(text[],oid)
function cstore_table_size(regclass)
```
```
\dy
List of event triggers
Name | Event | Owner | Enabled | Procedure | Tags
----------------------+-----------------+----------+---------+------------------------------+------
cstore_ddl_event_end | ddl_command_end | postgres | enabled | cstore_ddl_event_end_trigger |
cstore_drop_event | sql_drop | postgres | enabled | cstore_drop_trigger |
```
```
pg_restore: [archiver (db)] Error while PROCESSING TOC:
pg_restore: [archiver (db)] Error from TOC entry 3356; 3466 17447 EVENT TRIGGER cstore_ddl_event_end postgres
pg_restore: [archiver (db)] could not execute query: ERROR: event trigger "cstore_ddl_event_end" already exists
Command was: CREATE EVENT TRIGGER cstore_ddl_event_end ON ddl_command_end
EXECUTE PROCEDURE public.cstore_ddl_event_end_trigger();

pg_restore: [archiver (db)] Error from TOC entry 3357; 3466 17448 EVENT TRIGGER cstore_drop_event postgres
pg_restore: [archiver (db)] could not execute query: ERROR: event trigger "cstore_drop_event" already exists
Command was: CREATE EVENT TRIGGER cstore_drop_event ON sql_drop
EXECUTE PROCEDURE public.cstore_drop_trigger();

WARNING: errors ignored on restore: 2
```
Maybe is already fixed in 1.6, if yes... close it.

Thank's
David