Only write the px value in Show for Au

The integer Au value is mostly internal and does not make much sense.

Printing both values is very verbose and hurts readability of debug logs.

src/components/util/geometry.rs

@@ -79,8 +79,7 @@ impl Default for Au {
 
 impl fmt::Show for Au {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let Au(n) = *self;
-        write!(f, "Au(au={} px={})", n, to_frac_px(*self))
+        write!(f, "{}px", to_frac_px(*self))
     }}
 
 impl Add<Au,Au> for Au {