Remove |editable| in |FocusedNodeChanged|

Remove |editable| in |FocusedNodeChanged|

The logic regarding the parameter |editable| is duplicated.
It is used to remember that the current focus is on the input element
and to reset the context after the focus is lost or changed.

There are 2 functions in it.

1. |IMContextEfl::CancelComposition|
The function consists of |ResetIMFContext| and |ConfirmComposition|.
The former one is called through |RenderWidgetHostViewAura
::FocusedNodeChanged|->|InputMethodAuraLinux::ResetContext|
->|EflInputMethodContext::Reset|->|IMContextEfl::ResetIMFContext|.
When the mouse event or touch event which makes the focus change  occurred,
|RenderWidgetHostViewEventHandler::FinishImeCompositionSession|
is called and eventually |RenderWidgetHostImpl::ImeFinishComposingText|
which is the purpose of |IMContextEfl::ConfirmComposition| is invoked.
If the focused node is changed by TAB key, the commit signal is sended
by the platform so manual cancellation isn't needed.

2. |IMContextEfl::OnFocusOut|
When the focus is updated, through |InputMethodAuraLinux
::UpdateContextFocusState|->|EflInputMethodContext::UpdateFocus|,
|EflInputMethodContext::Blur| calls the function above.

So remove the codes related to the |editable| parameter.

Change-Id: I7f8f6bdb7039fcac47c595ba38508d670641f298
Signed-off-by: Hyomin Kim <hyoputer.kim@samsung.com>