Remove -webkit-user-drag

sky/engine/core/css/CSSProperties.in

 // This file specifies all the CSS properties we support and the necessary
 // information for our code generation. The various supported arguments
 // are described below with example usage
 
 // We should remove all those marked OBSOLETE now
 // We should remove all those marked LAYOUT once we have custom layout
 // We should remove all those marked ANIMATIONS once we have an animation system
 
 // - alias_for=other-property
 // Properties specifying alias_for do not get their own enum and instead map
@@ skipping 351 matching lines @@
 // ANIMATION
 transition-duration custom_all
 
 // ANIMATION
 transition-property custom_all
 
 // ANIMATION
 transition-timing-function custom_all
 
 // OBSOLETE
--webkit-user-drag
-
-// OBSOLETE
 -webkit-user-modify inherited
 
 // OBSOLETE
 -webkit-user-select inherited
 
 white-space inherited
 
 // LAYOUT
 width animatable, initial=initialSize, converter=convertLengthSizing
 
@@ skipping 107 matching lines @@
 -webkit-border-after longhands=-webkit-border-after-width;-webkit-border-after-style;-webkit-border-after-color
 -webkit-border-before longhands=-webkit-border-before-width;-webkit-border-before-style;-webkit-border-before-color
 -webkit-border-end longhands=-webkit-border-end-width;-webkit-border-end-style;-webkit-border-end-color
 // "-webkit-border-radius: 1px 2px" behaves as "border-radius: 1px / 2px"
 -webkit-border-radius longhands=border-top-left-radius;border-top-right-radius;border-bottom-right-radius;border-bottom-left-radius
 -webkit-border-start longhands=-webkit-border-start-width;-webkit-border-start-style;-webkit-border-start-color
 -webkit-text-emphasis longhands=-webkit-text-emphasis-style;-webkit-text-emphasis-color
 -webkit-text-stroke longhands=-webkit-text-stroke-width;-webkit-text-stroke-color
 -webkit-transform-origin longhands=-webkit-transform-origin-x;-webkit-transform-origin-y;-webkit-transform-origin-z
 transition longhands=transition-property;transition-duration;transition-timing-function;transition-delay