Remove custom language prefix from sites group form

Problem/Motivation

Currently when using auto masquerade, a prefix is set automatically which can be wrong if the destination site does not have the prefix configured for the language. This results in the editor landing on a 404 page.

Steps to reproduce

Create 2 sites with different default language settings then globally configured. Go to the sites tab on any content, the edit links with automasquerade are broken now.

Proposed resolution

Remove the prefix and add a site context to that links in sites_group.