Media Grid: remove Router code that doesn't actually ever run.

See #29121.

Built from https://develop.svn.wordpress.org/trunk@29443


git-svn-id: http://core.svn.wordpress.org/trunk@29221 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Media Grid: remove Router code that doesn't actually ever run.

See #29121.

Built from https://develop.svn.wordpress.org/trunk@29444


git-svn-id: http://core.svn.wordpress.org/trunk@29222 1a063a9b-81f0-0310-95a4-ce76da25c4cd