remove mainpage doxygen tag

sorting/non_recursive_merge_sort.cpp

@@ -5,7 +5,9 @@
  * A generic implementation of non-recursive merge sort.
  */
 #include <cstddef>  // for size_t
+#include <iostream>
 #include <utility>  // for std::move & std::remove_reference_t
+
 template <class Iterator>
 void merge(Iterator, Iterator, const Iterator, char[]);
 /// bottom-up merge sort which sorts elements in a non-decreasing order
@@ -83,15 +85,7 @@ template <class Iterator>
 void non_recursive_merge_sort(const Iterator first, const Iterator last) {
     non_recursive_merge_sort(first, last, last - first);
 }
-/**
- * @mainpage A demonstration of auto-generated documentation using Doxygen.
- * Currently, it only creates output for non_recursive_merge_sort.cpp, but if
- * it has proven its efficacy it can be expanded to other files.
- * The configuration file is named doxy.txt and has been auto-generated too.
- */
-// the remaining of this file is only for testing. It can erased to to convert
-// it into a header file for later re-use.
-#include <iostream>
+
 int main(int argc, char** argv) {
     int size;
     std::cout << "Enter the number of elements : ";