Add a few more [unwrap] calls to the FormulaManagerView.

Remove one assertion from ExpressionToFormulaVisitor as it is no longer true with wrapped formulas.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@15141 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c