Revisions UI: Remove the "To:" prefix from the header when viewing a single revision. Also prefix a revision field with a label.

props SergeyBiryukov, adamsilverstein, faishal. fixes #23903.

git-svn-id: https://core.svn.wordpress.org/trunk@23994 1a063a9b-81f0-0310-95a4-ce76da25c4cd