Remove g_bans global

[ranisalt]

Pull Request Prelude

• [x] I have followed proper The Forgotten Server code styling.
• [x] I have read and understood the contribution guidelines before making this PR.
• [x] I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

One less global state to deal with, and less code in headers. Moves IP ban code to server.cpp where it is actually used.