Inline internal function columns.

The internal function columns, used only as part of BNFC.Utils.table, is
relatively small after a prior simplification.

This commit inlines the definition of columns in the only place where it
is used.

source/src/BNFC/Utils.hs

@@ -168,10 +168,7 @@ table sep m = map (intercalate sep . zipWith pad widths) m
   where
   -- Column widths.
   widths :: [Int]
-  widths = columns maximum $ map (map length) m
-  -- Aggregate columns (works even for a ragged matrix with rows of different length).
-  columns :: ([a] -> b) -> [[a]] -> [b]
-  columns f = map f . transpose
+  widths = map maximum $ transpose $ map (map length) m
 
 -- * List utilities