CRM-12322 remove multisite specific ACL portion 

I don't know if this is a complete fix to CRM-12322 but it seems to improve it & based on the code I can understand that
1) the multisite clause says ' if user does not have any entries in acl_contact_cache, don't build the menu properly. I'm not sure when the menu is built but this seems to explain the somewhat 'unreliable' nature of the menu bug - as even after the cache is populated the menu doesn't instantly come right.

2) without this clause there is a clause further down to deal with ACLhook usage - which is what ACL Multisite is. This seems to deal adequately with the ACL scenario & simply looks to see an ACL hook is being applied. I assume this was added after the multisite check was put in

3) code is simplified by removing this block which is good.