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-common.go

@@ -18,7 +18,7 @@
 package cmd
 
 const (
-	storageRESTVersion       = "v40" // Add ReplicationState field
+	storageRESTVersion       = "v41" // Optimized DeleteVersions API
 	storageRESTVersionPrefix = SlashSeparator + storageRESTVersion
 	storageRESTPrefix        = minioReservedBucketPath + "/storage"
 )