Fix isPure to be superset of isOutputter.

This may cause some additional SIDEEFFECT warnings that previously were not shown.

src/V3Ast.cpp

@@ -801,7 +801,6 @@ AstNode* AstNode::cloneTreeIter(bool needPure) {
                          << this->warnMore()
                          << "... Suggest use a temporary variable in place of this expression");
         // this->v3fatalSrc("cloneTreePure debug backtrace");  // Comment in to debug where caused
-        // it
     }
     AstNode* const newp = this->clone();
     if (this->m_op1p) newp->op1p(this->m_op1p->cloneTreeIterList(needPure));