Remove default port API

Remove default port API

With the possibility of creating new ports for the whole lifetime of
a component, default ports aren't so useful and their name is
arbitrary. We don't need this for the 2.0 target.

The existing component classes are changed like so:

* debug-info.debug-info [filter]: one `in` input port and one `out`
  output port

* text.pretty [sink]: one `in` input port

* utils.dummy [sink]: one `in` input port

* utils.trimmer [filter]: one `in` input port and one `out` output port

* writer.writer [sink]: one `in` input port

Tests are updated accordingly.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>