Revert FontTransform::RotateAngle commit

This reverts commit 1b3414a.

That commits purpose was to provide coverage of a new FontTransform
enum element that was added to the plotters lib, but the element
was subsequently removed in plotters commit 6bd3004

Author: AE1020

src/canvas.rs

@@ -252,7 +252,6 @@ impl DrawingBackend for CanvasBackend {
             FontTransform::Rotate90 => 90.0,
             FontTransform::Rotate180 => 180.0,
             FontTransform::Rotate270 => 270.0,
-            FontTransform::RotateAngle(angle) => angle as f64,
         } / 180.0
             * std::f64::consts::PI;