Remove wrong assert to fix a debug crash with arguments object.
Remove wrong assert to fix a debug crash with arguments object.

We don't need to assert the existence of a length-property of the
arguments object because it is not a JSArray, but just a normal JSObject.

BUG=v8:1227
Review URL: http://codereview.chromium.org/7064020

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@8024 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh