relnotes: copy "next" to "5.6" and clear "next"

The same procedure as every year^Wcycle.

Differential Revision: https://phab.mercurial-scm.org/D9263

relnotes/next

@@ -1,12 +1,5 b''
 == New Features ==
 
- * `hg mv -A` can now be used with `--at-rev`. It behaves just like
-   `hg cp -A --at-rev`, i.e. it marks the destination as a copy of the
-   source whether or not the source still exists (but the source must
-   exist in the parent revision).
-
- * New revset predicate `diffcontains(pattern)` for filtering revisions
-   in the same way as `hg grep --diff pattern`.
 
 
 == New Experimental Features ==
@@ -23,7 +16,4 b''
 
 == Internal API Changes ==
 
- * `merge.update()` is now private (renamed to `_update()`). Hopefully
-   the higher-level functions available in the same module cover your
-   use cases.