PostgreSQL: How to DROP FUNCTION IF EXISTS without specifying parameters?

As of Postgres 10 you can drop functions by name only, as long as the names are unique to their schema.

Example:

drop function if exists Foo;

Documentation here.

In Postgres functions can be overloaded, so parameters are necessary to distinguish overloaded functions. To unambiguously identify a function you can put only types of its parameters.

DROP FUNCTION IF EXISTS Foo(INT);