TIF: Fix the Singapore content ratings

It is not that Singapore has two different rating systems. There is just one
rating system from Board of Film Censors but each broadcaster uses a different
subset of ratings. For example, Free-To-Air uses PG and PG13 while Pay TV uses
NC16 and M18 ratings in addition to the PG and PG13.

Bug: 17330613
Change-Id: I5a5e47706e7415f13a5e7dc9c00cc2c3c3763965