Reverted "Refs #16682 -- Tested transaction.atomic() with KeyboardInterrupt."

This reverts commit d895fc9a since the
test is problematic as described in the ticket.

tests/transactions/tests.py

-import os
-import signal
 import sys
 import threading
 import time
@@ -218,18 +216,6 @@ class AtomicTests(TransactionTestCase):
             transaction.savepoint_rollback(sid)
         self.assertQuerysetEqual(Reporter.objects.all(), ['<Reporter: Tintin>'])
 
-    @skipIf(sys.platform.startswith('win'), "Windows doesn't have signals.")
-    def test_rollback_on_keyboardinterrupt(self):
-        try:
-            with transaction.atomic():
-                Reporter.objects.create(first_name='Tintin')
-                # Send SIGINT (simulate Ctrl-C). One call isn't enough.
-                os.kill(os.getpid(), signal.SIGINT)
-                os.kill(os.getpid(), signal.SIGINT)
-        except KeyboardInterrupt:
-            pass
-        self.assertEqual(Reporter.objects.all().count(), 0)
-
 
 class AtomicInsideTransactionTests(AtomicTests):
     """All basic tests for atomic should also pass within an existing transaction."""