remove awkward 'delta' from ValueAnalysisState, along with all references; as of now, it does not really have a benefit anymore, as the speed-up is no longer relevant to justify this level of awkwardness

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14745 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c