Edited Unassigned: Remove AutoAdjustPlotMargins [10173]

This property can be redundant if the definition of `PlotMargins` is changed.
Set the default `PlotMargins` = (NaN,NaN,NaN,NaN), this should match AutoAdjustPlotMargins = true.
When a margin is NaN, the margin should be auto adjusted.
The `ActualPlotMargins` contains the actual values.