Force passing a cnx to run_all_tasks()

This has been deprecated for a while, make this mandatory.

entities.py

@@ -17,7 +17,6 @@
 
 """cubicweb-celerytask entity's classes"""
 import six
-import warnings
 
 import celery
 from celery.result import AsyncResult, from_serializable
@@ -43,12 +42,8 @@ def get_tasks():
     return _TEST_TASKS.copy()
 
 
-def run_all_tasks(cnx=None):
+def run_all_tasks(cnx):
     """Run all pending tasks (for use in cubicweb test mode)"""
-    if cnx is None:
-        warnings.warn('cnx argument should be specified to enable task '
-                      'workflow synchronisation', DeprecationWarning,
-                      stacklevel=2)
     results = {}
     # run all tasks and gather results.
     # Tasks can create other tasks, so run them until there is no one left.
@@ -56,7 +51,7 @@ def run_all_tasks(cnx=None):
         task_eid = list(_TEST_TASKS)[0]
         results[task_eid] = _TEST_TASKS.pop(task_eid).delay()
 
-    if cnx is not None and celery.current_app.conf.CELERY_ALWAYS_EAGER:
+    if celery.current_app.conf.CELERY_ALWAYS_EAGER:
         for task_eid, result in results.items():
             wf = cnx.entity_from_eid(task_eid).cw_adapt_to('IWorkflowable')
             transition = {