ci: remove cargo-audit

It's been replaced by cargo-deny in all modules.

Don't regenerate images for now, it's not a problem to keep it around
until the next images update round.

ci/install-rust.sh

@@ -22,5 +22,4 @@ if [ "$RUST_VERSION" = "stable" ]; then
   rustup component add rustfmt
   cargo install --force cargo-deny
   cargo install --force --git https://github.com/kbknapp/cargo-outdated
-  cargo install --force cargo-audit
 fi