all: remove descent padding from horizontal axis

Author: kortschak

axis.go

@@ -235,7 +235,6 @@ type horizontalAxis struct {
 // size returns the height of the axis.
 func (a horizontalAxis) size() (h vg.Length) {
 	if a.Label.Text != "" { // We assume that the label isn't rotated.
-		h += a.Label.TextStyle.FontExtents().Descent
 		h += a.Label.TextStyle.Height(a.Label.Text)
 		h += a.Label.Padding
 	}