Revert "Do not duplicate find-links already present in stack/slapos.cfg ."

This reverts commit 781c1a44.
Extended .cfg files are not cooperating, so += is unusable in [buildout]
section, even for find-links.

Conflicts:
	stack/erp5/buildout.cfg

stack/erp5/buildout.cfg

@@ -8,8 +8,11 @@ extensions =
   slapos.zcbworkarounds
   mr.developer
 
-find-links +=
+find-links =
+    http://www.nexedi.org/static/packages/source/slapos.buildout/
+    http://www.nexedi.org/static/packages/source/hexagonit.recipe.download/
     http://dist.repoze.org
+    http://www.nexedi.org/static/packages/source/
     http://www.owlfish.com/software/wsgiutils/download.html
 
 extends =