Princess: fix usage of static methods from Scala.

Author: kfriedberger

src/org/sosy_lab/java_smt/solvers/princess/PrincessFormulaCreator.java

@@ -546,7 +546,7 @@ private <R> R visitQuantifier(FormulaVisitor<R> visitor, BooleanFormula f, IQuan
 
     // substitute the bound variable with index 0 with a new variable, and un-shift the remaining
     // de-Bruijn indices, such that the next nested bound variable has index 0.
-    IFormula substitutedBody = IFormula.subst(body, asScalaList(substitutionVariable), -1);
+    IFormula substitutedBody = IExpression.subst(body, asScalaList(substitutionVariable), -1);
 
     return visitor.visitQuantifier(
         f,