removed SQS and IronMQ brokers for now

Both brokers are not atomic and cause all kinds of problems during testing. Needs more time.
Meanwhile I want to release the pluggable broker backend.

django_q/tests/tasks.py

@@ -1,7 +1,3 @@
-# simple countdown, returns nothing
-from time import sleep
-
-
 def countdown(n):
     while n > 0:
         n -= 1
@@ -26,11 +22,6 @@ def word_multiply(x, word=''):
     return len(word) * x
 
 
-def count_forever():
-    while True:
-        sleep(0.5)
-
-
 def get_task_name(task):
     return task.name