message: Remove unused `MoveMergeable` concept
diff: @@ -639,16 +639,6 @@ namespace ranges
  IndirectlyCopyable<I0, Out>,
  IndirectlyCopyable<I1, Out>>;
  - template<typename I0, typename I1, typename Out, typename C = ordered_less,
  - typename P0 = ident, typename P1 = ident>
  - using MoveMergeable = meta::strict_and<
  - InputIterator<I0>,
  - InputIterator<I1>,
  - WeaklyIncrementable<Out>,
  - IndirectRelation<C, projected<I0, P0>, projected<I1, P1>>,
  - IndirectlyMovable<I0, Out>,
  - IndirectlyMovable<I1, Out>>;
  -
  template<typename I, typename C = ordered_less, typename P = ident>
  using Sortable = meta::strict_and<
  ForwardIterator<I>,
  