RelNotes: remove the mention of !reinclusion

We will be postponing this to a later cycle.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/RelNotes/2.8.0.txt

@@ -294,11 +294,6 @@ notes for details).
    listing and sparse checkout selection areas in 2.7.0; the change
    that is responsible for the regression has been reverted.
 
- * Another try to improve the ignore mechanism that lets you say "this
-   is excluded" and then later say "oh, no, this part (that is a
-   subset of the previous part) is not excluded".  This has still a
-   known limitation, though.
-
  * Some codepaths used fopen(3) when opening a fixed path in $GIT_DIR
    (e.g. COMMIT_EDITMSG) that is meant to be left after the command is
    done.  This however did not work well if the repository is set to