ace2_inner: Delete special arrow key handling
ace2_inner: Delete special arrow key handling

I can't see any reason this would be necessary, and it appears to not
behave as intended (`scroll.scrollWhenPressArrowKeys()` is not invoked
after a continuously held arrow key is finally let up).

ether/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite,storytouch/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite