Remove now-defunct 8u and 11u builds

See https://github.com/AdoptOpenJDK/openjdk8-upstream-binaries#readme and https://github.com/AdoptOpenJDK/openjdk11-upstream-binaries#readme 🙇

To be 100% explicitly clear: 8u and 11u *are still maintained releases*, they are just no longer provided here.  Please find alternatives (Eclipse Temurin, etc) if you wish to continue using them.

Once Oracle stops publishing OpenJDK 18 builds, those will also be removed, and 19+ will be removed as soon as each release hits GA (as discussed previously).

From this point forward, our focus is on publishing only the EA builds from Oracle (since none of the other Java-providing official images currently do so).

Author: tianon