Eo: Remove eo_error_set() and clean up finalizer()

Eo: Remove eo_error_set() and clean up finalizer()

This is another cleanup in perparation for the Eo stable release.
This is no longer needed thanks to the proper error reporting with
eo_constructor()'s new return value.

The finalizer change cleans it up a bit so it catches more cases/issues.
This also means that the finalizer cleans up the object in all cases,
and not only some.

@feature.