Revert "Set pie chart face default toAngle to 180"

Unfortunately Quick Charts 5.70 doesn't draw a background unless the
end angle is 360. This has been fixed in Quick Charts 5.71 but as
Plasma 5.19 depends on 5.70 we need to revert this.

This reverts commit ee7536b214abb76abafb73fdbcc9a07dc3e78613.