[BUG] Remove Graph extension

## Describe the bug
The Graph extension was archived in 2025 after being deprecated since 2023.
See the archived page https://www.mediawiki.org/w/index.php?oldid=7692802

Graph is vulnerable to XSS exploitation and thus is not suitable for a public wiki. Furthermore, it is not currently maintained so it doesn't appear that someone will take up the mantle for restructuring it.
