Remove "Press back once more to exit" prompt

[ericwa]

I find these back button prompts cumbersome on Android, this PR just removes the feature. I didn't see a specific mention of them in Google's UI design guide, but I'm pretty sure they would be discouraged.
Not sure if you'll want this.. :)

[ildar]

Please don't merge this. The feature is good for users and that's the ultimate measure. Otherwise please suggest a replacement to prevent unintended app quitting, don't just throw something away. Just don't suggest a dialog asking if you really want to quit :)

[ericwa]

I can understand that, if you're used to the feature and mostly use apps that have it, then removing "tap again to quit" would be annoying and lead to exiting by accident.

On the other hand, for users who primarily use apps without "tap again to quit", it's a negative feature because tapping back to exit an activity becomes muscle memory, so when one app behaves differently it slows you down.

Maybe I could add a setting for this instead?

[eighthave]

I think spaRSS is a great app, but the "back again to Quit" thing always just aggravates me. The Android way to handle app quitting is to save state, and transparently resume. If there must be an quit/exit, then it should be a menu item.

I fully aware that there are use cases that cannot be addressed without a quit option, but I don't see any such use case in spaRSS.

[avengerx]

Instead of stripping out the option completely, why don't keep the default (ask to press twice to quit) but add a setting option to disable it? Then everyone can be happy.