MDL-29956 ims-cc - disabling export and cleaning some unused code

MDL-29956 ims-cc - disabling export and cleaning some unused code

This commits cleans some code (settings and dependencies)
and one file included previous by error.

Also it disables all the IMS-CC export feature by default, being
possible to enable it under demand by setting (@ config.php):

$CFG->enablebackupconverters = true;