Can't delete indexes that constraints depend on

Consider this DDL:

DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
( id serial
, title varchar(100)
, isbn varchar(13) NOT NULL
, copy_nr integer NOT NULL
, PRIMARY KEY (id)
, UNIQUE (isbn, copy_nr)
);

To reproduce:

* run this SQL to create the table
* reload (cmd+R)
* select `my_table`, choose `Structure`
* press the minus (`-`) button right of the index-definition
* press save changes

expected:

* The index will be dropped.

actual:
* I get an error, the index can't be dropped because there is still a constraint (`PostgreSQL said: cannot drop index my_table_pkey because constraint my_table_pkey on table my_table requires it
Hint: You can drop constraint my_table_pkey on table my_table instead.`). See

The same goes for the composite-index.

Reproduce the SQL setup, then use the Structure view on my_table and follow the index deletion through Save Changes. Check how primary-key and composite unique constraints are represented when their indexes are removed; done means the operation succeeds by handling the dependent constraint instead of issuing an invalid index drop.

Written by the indexing model from the issue text.