Increase or remove default JAVA_MAX_MEM

[josteinaj]

• https://github.com/daisy/pipeline-assembly/blob/master/src/main/resources/bin/pipeline2#L36
• https://github.com/daisy/pipeline-assembly/blob/master/src/main/resources/bin/pipeline2.bat#L78

It's currently set to 1G. Could we increase it to maybe 4G? Or if we just remove it, I think the system will pick a good default for us? My computer has 32 GB of RAM, and according to java -XX:+PrintFlagsFinal -version | grep HeapSize my max java memory defaults to 8G.

[bertfrees]

OK maybe it's best to just remove the default then. There's indeed not much point in setting it to a value lower than the default. Possibly we could generate a warning when a value is specified and it is less than 1G?

By the way, related: we should probably remove the $JAVA_MAX_PERM_MEM variable because the -XX:MaxPermSize has been removed in Java 8 which is our minimal Java requirement.