Replace Boost shared pointers

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src/ifcparse/parse.cpp

@@ -2750,7 +2750,7 @@ void file::remove_entity(const express::base& entity) {
 
     // Attention when running remove_entity inside a loop over a list of entities to be removed.
     // This invalidates the iterator. A workaround is to reverse the loop:
-    // boost::shared_ptr<aggregate_of_instance> entities = ...;
+    // std::shared_ptr<aggregate_of_instance> entities = ...;
     // for (auto it = entities->end() - 1; it >= entities->begin(); --it) {
     //    express::base *const inst = *it;
     //    model->remove_entity(inst);