Remove useless 'file is not empty' comments from __init__.py files #32506
Description
This is for #32501 and will make it easier to see which of the __init__.py files have an actual content.
Having this comment there appears to have been a workaround for hg, which is now irrelevant.
CC: @tscrim @fchapoton
Component: refactoring
Author: Matthias Koeppe
Branch/Commit: 1c106cd
Reviewer: Frédéric Chapoton
Issue created by migration from https://trac.sagemath.org/ticket/32506