tasks #7061 Delete old mapping

* Add instruction in README.mkd file in clean-up section
* Remove old generic mapping instruction for all project

Change-Id: I0a7afed900f9cf83ed7395c1dbfd38a1b848b0fe
Merge commit 'refs/changes/40/2640/2' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7061 Delete old mapping

Change-Id: If3c4f98652a9fb5f6f5f6f5b09dcd174dc912528
This is Tuleap 7.1.99.38

Change-Id: I26d00c5d52cb77151827bd94f3b198920f98870d