Revert "Use the online help  by default"

This reverts commit 1d5d116aa3e3f52b45c88ce3fe7d5f5cf07f9901.

There is a dialog telling the user that there is no local manual,
and that dialog has a button to use the online version. There is
no reason whatsoever to default to the online version.

Also, don't change the defaults in the custom OSX gimprc.