Remove component's initialization state flag

This "initializing" flag is now useless. It was used to make sure that
only the implementation side of a component could set the component's
private user data. This is now enforced by typing (component vs. private
component), and it is always okay to set a private component's user
data.

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