Fix request #7534 typo in artifact.rnc

Remove unneeded attribute format for static list

Change-Id: Icd35b831dc554baaad15866a8bb1ac959675e893
Merge commit 'refs/changes/35/3135/2' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fix request #7534 typo in artifact.rnc

Change-Id: Iab38d3a3533fda9e7171179891b8f189a4bc8a73
This is Tuleap 7.6.99.3

Change-Id: Ia66da29ebb6abab36b432a136c9f3d02f7585155