Revert "[FIX] core: close cursors open during tests"

Not necessary anymore thanks to commit
731b9f60ea.

The test cursors were leaked by the _check_accounting_configured()
function used to manually skip some tests.

After 731b9f6 the tests are skipped cleanly without
leaking cursors, so this became redundant with the reset()
function already present in the TransactionCase cleanups.

This reverts commit 57b14988b0.

openerp/tests/common.py

@@ -88,14 +88,7 @@ class BaseCase(unittest2.TestCase):
     """
 
     def cursor(self):
-        cr = self.registry.cursor()
-
-        @self.addCleanup
-        def close_cursor():
-            if not cr.closed:
-                cr.close()
-
-        return cr
+        return self.registry.cursor()
 
     def ref(self, xid):
         """ Returns database ID for the provided :term:`external identifier`,