CLDSRV-741: Fix comment about index

There is no DELETE it's a POST
There is a GET

Author: BourgoisMickael

lib/routes/routeBackbeat.js

@@ -342,7 +342,7 @@ GET /_/backbeat/lifecycle/<bucket name>?list-type=noncurrent
 GET /_/backbeat/lifecycle/<bucket name>?list-type=orphan
 POST /_/backbeat/index/<bucket name>?operation=add
 POST /_/backbeat/index/<bucket name>?operation=delete
-DELETE /_/backbeat/index/<bucket name>
+GET /_/backbeat/index/<bucket name>
 */
 
 function _getLastModified(locations, log, cb) {