[fix] System template cleanup. Fixes #4177

Remove unused code

This file tried to load 2 css files that do not exist. This PR removes the call to those files
[fix] Fixed broken TOS modal link. Fixes #4217
[fix] Making error message user-friendly (suggesting fix) and increasing recommended maximum upload size to 8 MB. Fixes #4210

Update warnings.php

Update en-GB.com_installer.ini