Fixed xenforo.css includes nonexistent template

[refael]

xenforo.css has this line:

<xen:include template="xenforo_facebook.css" />

There is no such template, it's actually `facebook.css`.

I guess when this is fixed, it can be removed from `login_bar_form` and `helper_login_form`, since xenforo.css is global for all pages.

 

[Mike]

I've removed the bad include -- it seems that this template did exist (last changed 1.0.1 potentially). However, I'm not currently planning on changing how the includes work so facebook.css will be included only when necessary.