Remove tags for comment client request time histogram in Datadog

According to someone from Datadog, this was generating tags like "knowledgeable_
people_who_put_this_course_together._this_is_harvard._you_can_t_tell_us_there_s_
a_shortage_of_editorial_talent." They say that they can handle tens or hundreds
of unique tags but not thousands. Given that we have a unique URL for each
thread, we can't even use that as a tag. Thus, all tags are removed for now
until we can determine whether there is a useful set of tags with small enough
cardinality. In light of this, I did not investigate why the long tag mentioned
above was being generated.

lms/lib/comment_client/utils.py

@@ -31,14 +31,9 @@ def merge_dict(dic1, dic2):
 def perform_request(method, url, data_or_params=None, *args, **kwargs):
     if data_or_params is None:
         data_or_params = {}
-    tags = [
-        "{k}:{v}".format(k=k, v=v)
-        for (k, v) in data_or_params.items() + [("method", method), ("url", url)]
-        if k != 'api_key'
-    ]
     data_or_params['api_key'] = settings.API_KEY
     try:
-        with dog_stats_api.timer('comment_client.request.time', tags=tags):
+        with dog_stats_api.timer('comment_client.request.time'):
             if method in ['post', 'put', 'patch']:
                 response = requests.request(method, url, data=data_or_params, timeout=5)
             else: