Remove legacy function group_getid_by_name()

Fix request #7211: Fatal error while accessing to a specific svn
revision.

This is a follow-up to commit #f1257e04bf4ccba9de6bba85aabc6038057f98d9
where we removed a bunch of require_once in order to save trees.
Unfortunately, there is edge case when legacy methods are used with an
obscur require chain. (We are far from the phpwiki spaghetti by the way)

The solution for this issue is to remove the legacy function and use the
dedicated object instead.

Change-Id: Ia4b45e55c85765d4689bb37b924271126ba84112
Merge commit 'refs/changes/64/2764/3' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  Remove legacy function group_getid_by_name()

Change-Id: Ib89500797b34c9495dc6f9d01973bd083e4d2e79
This is Tuleap 7.2.99.57

Change-Id: Id99f2e18b4b0c12baf4cb770c7d0829159ae2d84