kde-projects: Don't auto-filter git-repo's direct children.

Kind of a mouthful, but remove a filter that was added to avoid
automatically including an actual git repository's children that were
also git repositories. E.g. think of something like a SuperBuild git
module that also had its component git modules as logical children
within projects.kde.org.

This filter is unnecessary now that kdesrc-build supports both kde.org
metadata (kde-build-metadata/build-script-ignore) and user-configurable
module filtering (ignore-modules option).

More importantly this filter precludes many other desirable types of
group syntax (e.g. including all of kdebindings just by asking for
kdebindings).

So we remove the filter. The trouble I've seen so far is that it is
now rather difficult to build *only* kdelibs, since kde/kdelibs is a
logical parent of nepomuk-core, nepomuk-widgets, and kactivities. This
can be worked-around by using a normal single module declaration. E.g.

    module kdelibs
        repository kde:kdelibs
    end module

On the other hand, the recently-added config file option
"ignore-modules" should now remove any kde-projects modules that contain
a path component(s) matching the ignored module. You may have to be
specific with a given ignore atom for this reason (e.g. ignore
playground/libs, not 'libs' otherwise you'll also ignore
kdegraphics/libs at this point... though that was also true before this
commit).

BUG:321667