style(py): remove whitespace to satisfy style check

Satisfy the style check by removing one blank line from the two
blank lines that separate top-level function and class
definitions.

In this regard, our style checker seems to be in disagreement
with our style guide, which defers to the standard Python
practice of using two blank lines in such cases.

tools/expand_stamp_vars_test.py

@@ -22,6 +22,7 @@
 import io
 import unittest
 
+
 class FilterTest(unittest.TestCase):
   """A simple test of the expansion feature."""
 
@@ -40,5 +41,6 @@ def test_basic(self):
 
     self.assertEqual(ostream.getvalue(), golden)
 
+
 if __name__ == "__main__":
   unittest.main()