Update about page for new screenshot and new video encoding. Remove old screenshots directory. fixes #24832.

props lancewillett, markjaquith.

Merges [24942] to the 3.6 branch.



git-svn-id: http://core.svn.wordpress.org/branches/3.6@24943 1a063a9b-81f0-0310-95a4-ce76da25c4cd