PostgreSQL - Desactivar contrains

--Per previous comments, it should be a problem. That said, there is a command that may be what you're looking to - it'll set the constraints to deferred so they're checked on COMMIT, not on every delete. If you're doing just one big DELETE of all the rows, it won't make a difference, but if you're doing it in pieces, it will.
SET CONSTRAINTS ALL DEFERRED

--is what you are looking for in that case. Note that constraints must be marked as DEFERRABLE before they can be deferred. For example:
ALTER TABLE table_name
ADD CONSTRAINT constraint_uk UNIQUE(column_1, column_2)
DEFERRABLE INITIALLY IMMEDIATE;

--The constraint can then be deferred in a transaction or function as follows:
CREATE OR REPLACE FUNCTION f() RETURNS void AS
$BODY$
BEGIN
SET CONSTRAINTS ALL DEFERRED;

-- Code that temporarily violates the constraint...
-- UPDATE table_name ...
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;