Fix sources to remove errors and activation

Add "firefox/includes/mwc_2014_schedule.lang" to files without active status (activation view).

Remove es-AR, es-CL, and es-MX from slogans: as it is, we generate a warning for missing file on every loop and display the file in their dashboard. We can either remove locales or copy over the files in granary, I think the first option is cleaner and easier to maintain than having multiple files around with the same content.