This was previously removed without needing to. Adding it back to force
users to not emulate the page for previous versions of IE. The
imagetoolbar http-equiv tag was not restored as IE does not contain that
anymore since IE7. Also, the chome=1 has been removed from the
X-UA-Compatible content as ChromeFrame does not receive any further
updates since 2014 and is potentially broken.
PHPBB3-14136
The path to the admin style CSS is currently created with $phpbb_admin_path.
We should however use the path_helper to correctly link to this file in order
to have a correct link on pages like extensions
PHPBB3-12018
