Don't await for error_logger handlers to initialise

It will never be started on OTP 21.

The problem this piece of code originally was added to solve
is not very relevant now that we use Lager. Arguably connection
rate throttling should be enforced elsewhere, be it Ranch or a proxy/load balancer.

In any case, this particular implementation worked around an error_logger
issue that is no longer problematic for us, and eventually won't be problematic
for the entire ecosystem because OTP 21 introduced a completely new logger.

Cherry-picked per discussion with @dumbbell and @lukebakken.

[#157964874]

(cherry picked from commit a54b44f)
(cherry picked from commit a210d82)

Author: michaelklishin

src/rabbit_reader.erl

@@ -181,15 +181,6 @@
 start_link(HelperSup, Ref, Sock) ->
     Pid = proc_lib:spawn_link(?MODULE, init, [self(), HelperSup, Ref, Sock]),
 
-    %% In the event that somebody floods us with connections, the
-    %% reader processes can spew log events at error_logger faster
-    %% than it can keep up, causing its mailbox to grow unbounded
-    %% until we eat all the memory available and crash. So here is a
-    %% meaningless synchronous call to the underlying gen_event
-    %% mechanism. When it returns the mailbox is drained, and we
-    %% return to our caller to accept more connections.
-    gen_event:which_handlers(error_logger),
-
     {ok, Pid}.
 
 shutdown(Pid, Explanation) ->