media-sound/whipper: use non-deprecated pygobject

media-sound/whipper: use non-deprecated pygobject

whipper/extern/task/task.py uses pygobject:3 with a fallback to
pygobject:2. Prefer the modern version instead of the last rites
candidate.
This also gets rid of the gobject-introspection dep (pygobject:3
will pull it in), which had a wrong PYTHON_USEDEP (gobject-introspection
is a python-single-r1 ebuild and consumers mustn't USEDEP), which
will cause problems with an upcoming gobject-introspection bump,
as it drops python2 support - but it doesn't matter for consumers,
because it's only for its own use by the g-ir-scanner tool, so
python2 consumers will continue to work fine if they don't wrongly
PYTHON_USEDEP on this.

Package-Manager: Portage-2.3.62, Repoman-2.3.12
Signed-off-by: Mart Raudsepp <leio@gentoo.org>