Fix: onExtractedDeleteText deletes unintended region.

InputMethodService#onExtractedDeleteText doesn't reset composing
region and InputConnection#deleteSurroundingText deletes text around
the composing region. As a result, #onExtractedDeleteText can delete
unintended region of the text.
This happens when a user perform Drag&Drop or tap "Delete" in
SuggestionsPopup in full screen extracted mode.

Bug: 22440907
Bug: 27536702
Change-Id: I875f2919896f8ff453a77fb4a1b642ad78079b78