Clean-up the web-inspector autocompletion file

CSSMetadata.js should really be auto-generated as it is getting
stale super fast as we rename, remove and hack on the CSS engine.

This change started a grid patch but ended up cleaning flex and
'hyphens' usage too.

Review URL: https://chromiumcodereview.appspot.com/23653048

git-svn-id: svn://svn.chromium.org/blink/trunk@158032 bbb929c8-8fbe-4397-9dbb-9b2b20218538