Changed default skill rust setting from "vanilla" to "int"

A new player creating their first character sees "skill rust: XX%"
listed when selecting their int value, but in "vanilla" rust it
actually has no effect.

It's more intuitive for things, out of the box, to work the way the
character creation implies they do.
Merge pull request #7888 from rluddy/default-skill-rust-int

Changed default skill rust setting from "vanilla" to "int"