MNT: Use skipUnknowns in FMRIB configuration profile

funpack/configs/fmrib/processing.tsv

@@ -33,5 +33,7 @@ all_except,6150,6155,20001,20002,20003,20004,20199,40001,40002,40006,40011,40012
 41202,41203,41270,41271	removeIfSparse(minpres=10)
 
 # Drop columns which are correlated with other columns (the one
-# with more missing values is dropped).
-all	removeIfRedundant(0.99, 0.2)
+# with more missing values is dropped). If processing
+# unknown/uncategorised data fields, do not remove columns that
+# are redundant w.r.t. those unknowns/uncategorised.
+all	removeIfRedundant(0.99, 0.2, skipUnknowns=True)