ecore_main.c: Refactor purely duplicate ecore_main_fd_handler_file_add()

ecore_main.c: Refactor purely duplicate ecore_main_fd_handler_file_add()

Summary:
... to simply invoke `_ecore_main_fd_handler_add()`. The only difference appears to be the former sets `->file` to `EINA_TRUE`. So, we add that as a parameter.

You can consider this patch, and any other contributions I make to enlightenment, to be under the terms of whatever open source license governs that particular project, or at your option, the MIT license. Basically, if I'm uploading patches here, it's because I want them to be useful.

Test Plan: Should be pretty straightforward. I am in the process of doing a compile check.

Reviewers: #efl

Projects: #efl

Differential Revision: https://phab.enlightenment.org/D2302