Remove old jbosstools.test.jre vars from parent POM

In parent POM are still variables for old JDKs:
https://github.com/jbosstools/jbosstools-build/blob/master/parent/pom.xml#L81
like 5, 6 and 7.
We do not support these JDKs anymore, so its an artifact.
Unfortunately these variables are also defined in some ITests(server, fuse...). It needs to be carefully removed and all ITests must be checked, if it is ok.
These variables are also defined on Jenkins(dev-platform and PSI), so it needs to be removed there too.