Issue web-platform-tests#34493 - Removes webkitMaskBox* from the list of alias

As shown in whatwg/compat#202
there is currently no browsers implementing the mask-border-*,
which should be the equivalent.

They stand on their own and probably for now deserves a test
by themselves.

Author: karlcow

compat/css-style-declaration-alias-enumeration.html

@@ -41,12 +41,6 @@
   'webkitFlexWrap',
   'webkitJustifyContent',
   'webkitMask',
-  'webkitMaskBoxImage',
-  'webkitMaskBoxImageOutset',
-  'webkitMaskBoxImageRepeat',
-  'webkitMaskBoxImageSlice',
-  'webkitMaskBoxImageSource',
-  'webkitMaskBoxImageWidth',
   'webkitMaskClip',
   'webkitMaskComposite',
   'webkitMaskImage',