remove meaningless and redundant code

[hqh2010]

function sync_closed_cb "return TRUE" is meaningless and redundant, code style should consistent with elsewhere, ie: in function parse_generic_args exit without return value

[paralin]

This change is in itself meaningless, it doesn't make any difference to remove that statement.

[matthiasclasen]

It returns TRUE because its return type is gboolean.

Seems fine to me, and there's no need to change it.