Deprecate jdk-variant

A long time ago, we supported different "variants" of the JDK build, like "normal" and "embedded". The --with-jdk-variant and associated machinery has been kept in place, even though it's not doing anyting. Time to remove it.

I chose to keep the "-normal-" in the build output name so as not to break any scripts. But I'm willing to change this if someone has a clear opinion otherwise.