eldbus: simplify code by using helper that create future directly.

eldbus: simplify code by using helper that create future directly.

The new helper help replace call to eina_future_resolved and eina_future_rejected with
a scheduler lookup to just one function call.

Reviewed-by: Xavi Artigas <xavierartigas@yahoo.es>
Reviewed-by: Vitor Sousa da Silva <vitorsousa@expertisesolutions.com.br>
Differential Revision: https://phab.enlightenment.org/D7340