Remove validation swf checks in the release task.

The release-validate task checks for the existance of flashuploader.swf and io.swf. This pr removes those checks so that flash can be removed from the library without breaking automated builds. 
@ericf @triptych @reid 
The following prs are queued to be pushed upstream into dev-3.x as soon as this can be incorporated into the builds.
https://github.com/yui/yui3/issues/1153
https://github.com/yui/yui3/issues/1154
https://github.com/yui/yui3/issues/1155