Remove Signal(providing_args) argument b/c it is deprecated

RemovedInDjango40Warning: The providing_args argument is deprecated.
As it is purely documentational, it has no replacement. If you rely
on this argument as documentation, you can move the text to a code
comment or docstring.

Author: atodorov

django_comments/signals.py

@@ -9,13 +9,16 @@
 # discarded and a 400 response. This signal is sent at more or less
 # the same time (just before, actually) as the Comment object's pre-save signal,
 # except that the HTTP request is sent along with this signal.
-comment_will_be_posted = Signal(providing_args=["comment", "request"])
+# Arguments: "comment", "request"
+comment_will_be_posted = Signal()
 
 # Sent just after a comment was posted. See above for how this differs
 # from the Comment object's post-save signal.
-comment_was_posted = Signal(providing_args=["comment", "request"])
+# Arguments: "comment", "request"
+comment_was_posted = Signal()
 
 # Sent after a comment was "flagged" in some way. Check the flag to see if this
 # was a user requesting removal of a comment, a moderator approving/removing a
 # comment, or some other custom user flag.
-comment_was_flagged = Signal(providing_args=["comment", "flag", "created", "request"])
+# Arguments: "comment", "flag", "created", "request"
+comment_was_flagged = Signal()