Remove scaling from perspective correction

Scaling is applied at the end of all geometric transformations, so it
would be more appropriate outside of the perspective correction tool.
Such an implementation would also work better with the auto-fit feature.

rtengine/procparams.h

@@ -918,7 +918,6 @@ struct PerspectiveParams {
     double  camera_yaw;
     double  projection_pitch;
     double  projection_rotate;
-    double  projection_scale;
     double  projection_shift_horiz;
     double  projection_shift_vert;
     double  projection_yaw;