Dashboard columns:

* Improve responsive breakpoints for.
* Remove obsolete network admin option.
* Remove unnecessary JS.

props SergeyBiryukov, kraftbj, lessbloat. fixes #26074.

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git-svn-id: http://core.svn.wordpress.org/trunk@26292 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Make ratings stars 20px to match dashicons native size so they're crisp on all screens. See #26170, props melchoyce.
Built from https://develop.svn.wordpress.org/trunk@26393


git-svn-id: http://core.svn.wordpress.org/trunk@26293 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't show the Activity widget on the Network Admin Dashboard. props ocean90. fixes #26184.

Built from https://develop.svn.wordpress.org/trunk@26394


git-svn-id: http://core.svn.wordpress.org/trunk@26294 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Move thickbox styles from wp-admin.css to thickbox.css. Remove old png close icons. Fixes #26178.


Built from https://develop.svn.wordpress.org/trunk@26395


git-svn-id: http://core.svn.wordpress.org/trunk@26295 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove the new thickbox styles from wp-admin.css. See #26178
Built from https://develop.svn.wordpress.org/trunk@26396


git-svn-id: http://core.svn.wordpress.org/trunk@26296 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add some deleted images to the `$_old_files` array. see [26391], [26395], #26232, #26178.

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git-svn-id: http://core.svn.wordpress.org/trunk@26297 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Make sure WP_Editor and Thickbox styles have Dashicons as a dependency, as they can be used on the front. props johnjamesjacoby. fixes #26236.

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git-svn-id: http://core.svn.wordpress.org/trunk@26298 1a063a9b-81f0-0310-95a4-ce76da25c4cd