Merge pull request #15544 from bangerth/affine-constraints-3

Simplify constructors/operators of AffineConstraints::ConstraintLine.

diff --cc include/deal.II/lac/affine_constraints.h
index f5c77b93a5957740634ee4d94a6cca3cc88354a7,bdb4671b17f4986d75fe3361716cc9ddf01d7f3e..2eed5643f0ed3bde21d9ef3b10575e240f1d9e26
--- 1/include/deal.II/lac/affine_constraints.h
--- 2/include/deal.II/lac/affine_constraints.h
+++ b/include/deal.II/lac/affine_constraints.h
@@@ -1664,10 -1669,33 +1669,15 @@@ public
      /**
       * Copy assignment.
       */
-     template <typename ConstraintLineType>
      ConstraintLine &
-     operator=(const ConstraintLineType &other);
+     operator=(const ConstraintLine &other) = default;
+ 
+     /**
+      * Move assignment.
+      */
+     ConstraintLine &
+     operator=(ConstraintLine &&other) noexcept = default;
  
 -    /**
 -     * This operator is a bit weird and unintuitive: it compares the line
 -     * numbers of two lines. We need this to sort the lines; in fact we could
 -     * do this using a comparison predicate.  However, this way, it is easier,
 -     * albeit unintuitive since two lines really have no god-given order
 -     * relation.
 -     */
 -    bool
 -    operator<(const ConstraintLine &) const;
 -
 -    /**
 -     * This operator is likewise weird: it checks whether the line indices of
 -     * the two operands are equal, irrespective of the fact that the contents
 -     * of the line may be different.
 -     */
 -    bool
 -    operator==(const ConstraintLine &) const;
 -
      /**
       * Determine an estimate for the memory consumption (in bytes) of this
       * object.