That, unfortunately, doesn't seem to work on the Android client (did that for the webapp). I'd give the app a bad rating for becoming more and more crappy, but I have no G+ account, cannot have a G+ account and therefor are unable to participate..
I disabled it on the web client and those labels do not appear on the Android app for me.
Additionally, you can disable the promotions tab individually. I just have "Updates" and "Forums". For now, it seems very easy to opt out.
For now.
Which is where we currently live, so that's good.
I think people are mad because it seems inevitable that, like all other new Gmail features/UI changes/etc., it will become mandatory within less than a year.
How do you do that?
Click on the + sign next to the tabs. Uncheck everything except "Primary" (which you can't uncheck anyway)
You know what's funny? You do that and when you look there are still unread things in there that it pulls from the inbox. Once you dispose of them in the inbox, they do disappear, though.
There's actually a number of different inbox layouts available in Settings.