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-client.go

@@ -590,7 +590,7 @@ func (client *storageRESTClient) Delete(ctx context.Context, volume string, path
 }
 
 // DeleteVersions - deletes list of specified versions if present
-func (client *storageRESTClient) DeleteVersions(ctx context.Context, volume string, versions []FileInfo) (errs []error) {
+func (client *storageRESTClient) DeleteVersions(ctx context.Context, volume string, versions []FileInfoVersions) (errs []error) {
 	if len(versions) == 0 {
 		return errs
 	}