Clean up plugins.php with regards to recently edited files, deactivations, and...

Clean up plugins.php with regards to recently edited files, deactivations, and the network admin. see #20468, #20104.
 * Limit recently_activated to the site dashboard, and properly remove bulk-activated plugins from the array.
 * Remove code used from before the network admin, such as the unused 'network' plugin_status.
 * Don't try to deactivate a plugin already deactivated.
 * Use more specific caps (manage_network_plugins) rather than is_super_admin().



git-svn-id: https://core.svn.wordpress.org/trunk@20525 1a063a9b-81f0-0310-95a4-ce76da25c4cd