Doc: Removed reference to deprecated \badcode command.

QDoc doesn't differentiate between \badcode and \code. They both look
the same in the output.

Change-Id: Ia0580f7d664ad5e33b48d6511dac7c61349cacce
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>