Don't load legacy gadget scripts
The time has come to stop supporting legacy gadgets that haven't
migrated to ResourceLoader yet.
For many Gadgets, migrating to ResourceLoader will be as easy
as adding "[ResourceLoader]" to its definition on MediaWiki:Gadgets-definition.
However for older gadgets, they may need more maintenance. Though
similarly they may've already been malfunctioning silently.
The most common techniques used by legacy scripts, and what their