CDesignatorVisitor and CSimpleDeclarationVisitor should not inherit from CExpressionVisitor, because CDesignators and CSimpleDeclarations are not CExpressions.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13572 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c