Remove .inIme state from CE Surface

The .inIme flag shows whether we have seen a compositionstart event with no
subsequent compositionend event. Unfortunately, this does not give any useful
guarantees about IME state (in particular, you can't tell whether there's a
candidate window open by looking at this). Therefore, we remove this flag and
change the way we handle IMEs.

Change-Id: If54ac913c891965ba1e647a1101c7d442363e225
Merge "Remove .inIme state from CE Surface"