Remove stale backend comment from routeBackbeat test.

Drop a legacy comment left from Ceph-era behavior to avoid ambiguity in multipart upload tagging tests.

Author: benzekrimaha

tests/multipleBackend/routes/routeBackbeat.js

@@ -3052,7 +3052,6 @@ describe('backbeat routes', () => {
     describeIfLocationAws('backbeat multipart upload operations (external location)', function test() {
         this.timeout(10000);
 
-        // The test backend does not support putting tags during initiate MPU.
         it('should put tags if the source is AWS and tags are ' +
             'provided when initiating the multipart upload', done => {
             const awsKey = uuidv4();