Simplify ResetCache() test.

src/ZODB/tests/testZODB.py

@@ -143,15 +143,12 @@ class ZODBTests(unittest.TestCase):
         # ought to be linked to it rather than the old cache.
         self.populate()
         conn = self._db.open()
-        try:
         conn.root()
         self.assert_(len(conn._cache) > 0)  # Precondition
         conn._resetCache()
         self.assertEqual(len(conn._cache), 0)
         self.assert_(conn._incrgc == conn._cache.incrgc)
         self.assert_(conn.cacheGC == conn._cache.incrgc)
-        finally:
-            conn.close()
 
     def checkLocalTransactions(self):
         # Test of transactions that apply to only the connection,