Remove unused RDS CA cert bundles.

We're not using these and we're unlikely to any time soon. It's also
easy to add them back in if we did want them later.

Dockerfile

@@ -24,11 +24,6 @@ FROM --platform=$TARGETPLATFORM scratch
 COPY --from=builder /src/router /bin/router
 COPY --from=builder /usr/share/ca-certificates /usr/share/ca-certificates
 COPY --from=builder /etc/ssl /etc/ssl
-# TODO: remove rds-combined-ca-bundle.pem once app is using global-bundle.pem.
-ADD https://s3.amazonaws.com/rds-downloads/rds-combined-ca-bundle.pem \
-    /etc/ssl/certs/rds-combined-ca-bundle.pem
-ADD https://truststore.pki.rds.amazonaws.com/global/global-bundle.pem \
-    /etc/ssl/certs/rds-global-bundle.pem
 USER 1001
 CMD ["/bin/router"]
 LABEL org.opencontainers.image.source="https://github.com/alphagov/router"