Delete QEvent::InputMethod handling in FakeVimHandler::eventFilter()

The head keys handling is not needed because IBusEngineSimple handles
compose keys.
Also the length of QInputMethodEvent.commitString() is not one and
prevent users from auto-complettions.

Change-Id: Ieb0022add243829340797954e7d48ca71af2c249
Reviewed-by: hjk <hjk121@nokiamail.com>