BUG: Import joblib modules in cluster outlier removal script

Import `joblib` modules in cluster outlier removal script.

Fixes:
```
File /bin/wm_cluster_remove_outliers.py, line 256, in main
  logtrs = Parallel(n_jobs=number_of_jobs, verbose=0)(
NameError: name 'Parallel' is not defined
```

Inadvertently removed in commit f66b337.

bin/wm_cluster_remove_outliers.py

@@ -5,6 +5,7 @@
 import glob
 import os
 import shutil
+from joblib import Parallel, delayed
 
 import numpy as np
 import vtk