[doxygen] Fix small Doxygen errors.

dune/common/shared_ptr.hh

@@ -57,7 +57,6 @@ namespace Dune
 
   /**
      @brief Convert a stack-allocated object to a shared_ptr:
-     @relates shared_ptr
      @code
           int i = 10;
           shared_ptr<int> pi = stackobject_to_shared_ptr(i);
@@ -71,7 +70,6 @@ namespace Dune
 
   /**
      @brief Convert a stack object to a shared_ptr of a base class
-     @relates shared_ptr
      @code
           class A {};
           class B : public A {};

dune/common/std/utility.hh

@@ -50,9 +50,7 @@ namespace Dune
     // index_sequence
     // --------------
 
-    /** \fn index_sequence
-     *
-     *  \brief a function similar to std::index_sequence to be introduced in
+    /** \brief a function similar to std::index_sequence to be introduced in
      *         C++14
      *
      *  \tparam  ...Ints  a non-type parameter pack