v3.3.0: Remove trailing commas to avoid black expanding code

From black 20.8b0's changelog:

```
re-implemented support for explicit trailing commas: now it works
consistently within any bracket pair, including nested structures (#1288
and duplicates)
```

We have lots of trailing commas throughout our source code and it causes
changes like this:

```
-    print('Brambox: %r, %r' % (brambox.__version__, brambox.__file__,))
+    print(
+        'Brambox: %r, %r'
+        % (
+            brambox.__version__,
+            brambox.__file__,
+        )
+    )
```

which adds lots of lines for no reason.  There are more extreme cases that make
the code less readable after black reformats the code.  The only way to avoid
this is to remove trailing commas.