Media Grid: Use an existing string for posts without a title.

see #24716.
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git-svn-id: http://core.svn.wordpress.org/trunk@29271 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Some pre-commit cleanup of media-grid.js and media-views.js
Built from https://develop.svn.wordpress.org/trunk@29494


git-svn-id: http://core.svn.wordpress.org/trunk@29272 1a063a9b-81f0-0310-95a4-ce76da25c4cd