remove double reads delete versions (#13544)

deleting collection of versions belonging
to same object, we can avoid re-reading
the xl.meta from the disk instead purge
all the requested versions in-memory,

the tradeoff is to allocate a map to de-dup
the versions, allow disks to be read only
once per object.

additionally reduce the data transfer between
nodes by shortening msgp data values.

cmd/storage-rest-server.go

@@ -643,7 +643,7 @@ func (s *storageRESTServer) DeleteVersionsHandler(w http.ResponseWriter, r *http
 		return
 	}
 
-	versions := make([]FileInfo, totalVersions)
+	versions := make([]FileInfoVersions, totalVersions)
 	decoder := msgp.NewReader(r.Body)
 	for i := 0; i < totalVersions; i++ {
 		dst := &versions[i]