Clean up .classpath files

Some .classpath files still contain references to SCALA_CONTAINER and
SCALA_COMPILER_CONTAINER which are not needed anymore. Furthermore
sdt.core explicitly references JavaSE-1.6 as its runtime environment
which shoudn't be included either because this doesn't allow a JRE
independent build.

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__DO NOT MERGE YET__

I also removed the reference to `org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType` because I couldn't find out what this does. The Javadoc of this class does not give more information. Does someone know what this reference mean?

Furthermore `test-workspace` contain references to JavaSE-1.6 as well. I will append the changes to these files once I found out what `StandardVMType` is doing.