efl-mono: Use Efl.Ui.Win API instead of Elm.Policy

efl-mono: Use Efl.Ui.Win API instead of Elm.Policy

Summary:
This removes another bit of legacy API from the C# bindings.
This also reverts "elm: Put back Policy and Policy_Quit in EO files"
(a9132a9a66955608e913bb1228e4adb371310b09) so that these two Elm enums are
definitely out of the EO files.

Test Plan:
Everything, including mono bindings, continue to build.
At runtime, C# apps still exit when all windows are closed.

Reviewers: lauromoura, vitor.sousa, q66

Reviewed By: q66

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8890