Don't treat width and height as shorthands in CSSShorthands.in

Currently CSSShorthands.in considers width and height to be shorthands,
although in regular css they are not shorthands and the behaviour is only
for parsing viewport descriptors. Removing this behaviour will make it
easier to merge the css property related .in files.

Having width and height in the shorthands system was added in:
https://codereview.chromium.org/16161005

Review URL: https://codereview.chromium.org/388153004

git-svn-id: svn://svn.chromium.org/blink/trunk@178132 bbb929c8-8fbe-4397-9dbb-9b2b20218538