Drop optional control modules load and unload

The optionnal control modules are loaded and unloaded through modules
dependencies by modprobe or libkmod. Trying to load them manually leads
to spurious log messages and slows down the sessiond startup.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>