In places where we call UnsafeFormulaManager.getArg(),
we can now usually expect to get correctly typed formula objects back,
so we do not need to overwrite the type of the returned object.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13697 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c