combobox: "return" key handled correctly and removed unreachable code.

combobox: "return" key handled correctly and removed unreachable code.

Summary:

_key_action_activate was triggered when "return" was pressed, _key_action_move
contained the "return" key handling, which is unreachable code.
@fix T3075 (1st point).

Signed-off-by: divyesh purohit <div.purohit@samsung.com>
Test Plan: please run combobox example in elementary_test

Reviewers: shilpasingh, cedric, raster

Subscribers: rajeshps, govi

Maniphest Tasks: T3075

Differential Revision: https://phab.enlightenment.org/D3599

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>