Use eina_file_unlink() instead of unlink()

[joaoantoniocardoso]

The unlink() function is being used all over the place where eina_file_unlink() would possibly fit better.

Note that here I first used a macro to perform the work, so I am still analyzing if it makes sense. For example in src/bin/edje there are several uses of unlink() that cannot be directly changed to eina_file_unlink() or it won't compile, so I didn't add to this batch.