Move Press This styles from press-this.php to wp-admin.css

[SergeyBiryukov]

Background: #19725

Replying to nacin:

This was done with a simple <style> block to prevent the need to ship the giant wp-admin.dev.css and wp-admin.css files in the 3.3.1 partial build. (We've already gone this far without a change.)

In 3.4, this should be cleaned up and merged into the main stylesheet.

In [19671]:

Merge Press This inline styles into wp-admin.css. fixes #19735.