Multisite: Remove redundant `is_super_admin()` when checking for `edit_others_posts`.

The super admin on multisite as well as the administrator on non-multisite both have this capability already. For custom post types using different capabilities this change ensures that only users with that capability have permissions.

Fixes #39059. See #37616.

Built from https://develop.svn.wordpress.org/trunk@39539


git-svn-id: https://core.svn.wordpress.org/trunk@39479 1a063a9b-81f0-0310-95a4-ce76da25c4cd