Remove old POM files

These didn't even work anymore, as the Log4j dependency was missing
Readd releases jar

The build script simply adds all files together in one zip.

I have tried using shadowJar for this (several times!), but it simply
didn't work: the forgeSrc dependency was always missing. Now it simply
uses a few methods to repackage the zip files.
Don't clean everything between each build

Doing this makes it almost impossible to launch the Forge version from
your IDE, as the necessary Minecraft files are removed every time you
use the gradle script.
Only generate IDE files for Java modules

- Remove archivesBaseName in releases/build.gradle. This property is not
needed as it is not a Java module. It's even deprecated on
non-Java-modules.